Mississippi Power (MSPWP) 10-Q 1 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Document Information [Line Items]
Entity Registrant Name	SOUTHERN CO
Entity Central Index Key	0000092122
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	1,040,295,732
ALABAMA POWER CO
Document Information [Line Items]
Entity Registrant Name	ALABAMA POWER CO
Entity Central Index Key	0000003153
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	30,537,500
GEORGIA POWER CO
Document Information [Line Items]
Entity Registrant Name	GEORGIA POWER CO
Entity Central Index Key	0000041091
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	9,261,500
MISSISSIPPI POWER CO
Document Information [Line Items]
Entity Registrant Name	MISSISSIPPI POWER CO
Entity Central Index Key	0000066904
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	1,121,000
SOUTHERN POWER CO
Document Information [Line Items]
Entity Registrant Name	SOUTHERN POWER CO
Entity Central Index Key	0001160661
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	1,000
SOUTHERN Co GAS
Document Information [Line Items]
Entity Registrant Name	SOUTHERN Co GAS
Entity Central Index Key	0001004155
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding	100

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Revenues:
Total operating revenues	$ 5,412	$ 6,372
Operating Expenses:
Other operations and maintenance	1,312	1,451
Depreciation and amortization	751	769
Taxes other than income taxes	329	355
Estimated loss on plants under construction	2	44
Gain on dispositions, net	(2,497)	0
Total operating expenses	1,721	4,996
Operating Income (Loss)	3,691	1,376
Other Income and (Expense):
Allowance for equity funds used during construction	32	30
Earnings from equity method investments	48	41
Interest expense, net of amounts capitalized	(430)	(458)
Other income (expense), net	78	60
Total other income and (expense)	(272)	(327)
Earnings (Loss) Before Income Taxes	3,419	1,049
Income taxes	1,360	113
Consolidated net income (loss)	2,059	936
Dividends on preferred stock of subsidiaries	4	4
Net loss attributable to noncontrolling interests	(29)	(6)
Net Income (Loss)	$ 2,084	$ 938
Earnings per share -
Basic (in dollars per share)	$ 2.01	$ 0.93
Diluted (in dollars per share)	$ 1.99	$ 0.92
Average number of shares of common stock outstanding (in millions)
Basic (in shares)	1,038	1,011
Diluted (in shares)	1,045	1,016
Retail electric revenues
Operating Revenues:
Total operating revenues	$ 3,084	$ 3,568
Wholesale electric revenues
Operating Revenues:
Total operating revenues	499	623
Other electric revenues
Operating Revenues:
Total operating revenues	168	161
Natural gas
Operating Revenues:
Total operating revenues	1,474	1,607
Operating Expenses:
Total cost of natural gas	686	720
Other
Operating Revenues:
Total operating revenues	187	413
Operating Expenses:
Total cost of natural gas	118	289
Fuel
Operating Expenses:
Total cost of natural gas	850	1,101
Purchased power
Operating Expenses:
Total cost of natural gas	170	267
ALABAMA POWER CO
Operating Revenues:
Total operating revenues	1,408	1,473
Operating Expenses:
Other operations and maintenance	409	387
Depreciation and amortization	199	189
Taxes other than income taxes	103	98
Total operating expenses	1,070	1,101
Operating Income (Loss)	338	372
Other Income and (Expense):
Allowance for equity funds used during construction	14	13
Interest expense, net of amounts capitalized	(83)	(79)
Other income (expense), net	14	5
Total other income and (expense)	(55)	(61)
Earnings (Loss) Before Income Taxes	283	311
Income taxes	62	82
Consolidated net income (loss)	221	229
Dividends on preferred stock of subsidiaries	4	4
Net Income (Loss)	217	225
ALABAMA POWER CO | Retail electric revenues
Operating Revenues:
Total operating revenues	1,213	1,285
ALABAMA POWER CO | Wholesale electric revenues
Operating Revenues:
Total operating revenues	61	74
ALABAMA POWER CO | Other
Operating Revenues:
Total operating revenues	74	63
ALABAMA POWER CO | Fuel
Operating Expenses:
Total cost of natural gas	301	326
ALABAMA POWER CO | Purchased power
Operating Expenses:
Total cost of natural gas	37	64
ALABAMA POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	60	51
ALABAMA POWER CO | Purchased power, affiliates
Operating Expenses:
Total cost of natural gas	21	37
GEORGIA POWER CO
Operating Revenues:
Total operating revenues	1,833	1,961
Operating Expenses:
Other operations and maintenance	446	408
Depreciation and amortization	240	228
Taxes other than income taxes	106	108
Total operating expenses	1,385	1,448
Operating Income (Loss)	448	513
Other Income and (Expense):
Interest expense, net of amounts capitalized	(96)	(106)
Other income (expense), net	40	38
Total other income and (expense)	(56)	(68)
Earnings (Loss) Before Income Taxes	392	445
Income taxes	81	93
Consolidated net income (loss)	311	352
Net Income (Loss)	311	352
GEORGIA POWER CO | Retail electric revenues
Operating Revenues:
Total operating revenues	1,668	1,798
GEORGIA POWER CO | Wholesale electric revenues
Operating Revenues:
Total operating revenues	29	44
GEORGIA POWER CO | Other
Operating Revenues:
Total operating revenues	133	109
GEORGIA POWER CO | Fuel
Operating Expenses:
Total cost of natural gas	299	412
GEORGIA POWER CO | Purchased power
Operating Expenses:
Total cost of natural gas	118	121
GEORGIA POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	3	10
GEORGIA POWER CO | Purchased power, affiliates
Operating Expenses:
Total cost of natural gas	176	171
MISSISSIPPI POWER CO
Operating Revenues:
Total operating revenues	287	302
Operating Expenses:
Other operations and maintenance	59	75
Depreciation and amortization	48	41
Taxes other than income taxes	26	28
Estimated loss on plants under construction	2	44
Total operating expenses	231	295
Operating Income (Loss)	56	7
Other Income and (Expense):
Interest expense, net of amounts capitalized	(17)	(19)
Other income (expense), net	5	1
Total other income and (expense)	(12)	(18)
Earnings (Loss) Before Income Taxes	44	(11)
Income taxes	7	(4)
Consolidated net income (loss)	37	(7)
Net Income (Loss)	37	(7)
MISSISSIPPI POWER CO | Retail electric revenues
Operating Revenues:
Total operating revenues	203	194
MISSISSIPPI POWER CO | Wholesale electric revenues
Operating Revenues:
Total operating revenues	57	68
MISSISSIPPI POWER CO | Other
Operating Revenues:
Total operating revenues	5	6
MISSISSIPPI POWER CO | Fuel
Operating Expenses:
Total cost of natural gas	93	98
MISSISSIPPI POWER CO | Purchased power
Operating Expenses:
Total cost of natural gas	3	9
MISSISSIPPI POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	22	34
SOUTHERN POWER CO
Operating Revenues:
Total operating revenues	443	509
Operating Expenses:
Other operations and maintenance	84	93
Depreciation and amortization	119	114
Taxes other than income taxes	11	12
Total operating expenses	383	449
Operating Income (Loss)	60	60
Other Income and (Expense):
Interest expense, net of amounts capitalized	(44)	(47)
Other income (expense), net	2	3
Total other income and (expense)	(42)	(44)
Earnings (Loss) Before Income Taxes	18	16
Income taxes	(9)	(99)
Consolidated net income (loss)	27	115
Net loss attributable to noncontrolling interests	(29)	(6)
Net Income (Loss)	56	121
SOUTHERN POWER CO | Wholesale electric revenues
Operating Revenues:
Total operating revenues	352	424
SOUTHERN POWER CO | Other
Operating Revenues:
Total operating revenues	4	2
SOUTHERN POWER CO | Fuel
Operating Expenses:
Total cost of natural gas	145	169
SOUTHERN POWER CO | Purchased power
Operating Expenses:
Total cost of natural gas	24	61
SOUTHERN POWER CO | Wholesale revenues, affiliates
Operating Revenues:
Total operating revenues	87	83
SOUTHERN Co GAS
Operating Revenues:
Total operating revenues	1,474	1,639
Operating Expenses:
Other operations and maintenance	235	276
Depreciation and amortization	118	129
Taxes other than income taxes	82	77
Goodwill impairment	0	42
Total operating expenses	1,121	1,251
Operating Income (Loss)	353	388
Other Income and (Expense):
Earnings from equity method investments	48	42
Interest expense, net of amounts capitalized	(59)	(59)
Other income (expense), net	5	12
Total other income and (expense)	(6)	(5)
Earnings (Loss) Before Income Taxes	347	383
Income taxes	77	104
Consolidated net income (loss)	270	279
Net Income (Loss)	270	279
SOUTHERN Co GAS | Natural gas
Operating Revenues:
Total operating revenues	1,476	1,631
Operating Expenses:
Total cost of natural gas	686	720
SOUTHERN Co GAS | Other
Operating Revenues:
Total operating revenues	0	32
Operating Expenses:
Total cost of natural gas	0	7
SOUTHERN Co GAS | Alternative revenue programs
Operating Revenues:
Total operating revenues	$ (2)	$ (24)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Alternative revenue programs
Total operating revenues	$ (2)	$ (24)
SOUTHERN Co GAS
Excise taxes collected	$ 55	$ 51

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net income (loss)	$ 2,059	$ 936
Qualifying hedges:
Changes in fair value, net of tax	(28)	47
Reclassification adjustment for amounts included in net income, net of tax	28	(19)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	0	2
Total other comprehensive income (loss)	0	30
Comprehensive Income (Loss)	2,059	966
Less:
Dividends on preferred stock of subsidiaries	4	4
Comprehensive loss attributable to noncontrolling interests	(29)	(6)
Comprehensive Income (Loss) Attributable to Parent	2,084	968
ALABAMA POWER CO
Net income (loss)	221	229
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	1	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1
Comprehensive Income (Loss)	222	230
Less:
Dividends on preferred stock of subsidiaries	4	4
GEORGIA POWER CO
Net income (loss)	311	352
Qualifying hedges:
Reclassification adjustment for amounts included in net income, net of tax	1	1
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	1	1
Comprehensive Income (Loss)	312	353
MISSISSIPPI POWER CO
Net income (loss)	37	(7)
Qualifying hedges:
Changes in fair value, net of tax	0	(1)
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	0	(1)
Comprehensive Income (Loss)	37	(8)
SOUTHERN POWER CO
Net income (loss)	27	115
Qualifying hedges:
Changes in fair value, net of tax	(29)	48
Reclassification adjustment for amounts included in net income, net of tax	25	(24)
Pension and other postretirement benefit plans:
Total other comprehensive income (loss)	(4)	24
Comprehensive Income (Loss)	23	139
Less:
Comprehensive loss attributable to noncontrolling interests	(29)	(6)
Comprehensive Income (Loss) Attributable to Parent	52	145
SOUTHERN Co GAS
Net income (loss)	270	279
Qualifying hedges:
Changes in fair value, net of tax	0	1
Reclassification adjustment for amounts included in net income, net of tax	0	2
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax	(1)	(1)
Total other comprehensive income (loss)	(1)	2
Comprehensive Income (Loss)	$ 269	$ 281

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Qualifying hedges:
Changes in fair value, tax	$ (9)	$ 16
Reclassification adjustment for amounts included in net income, tax	9	(6)
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, tax	0	0
ALABAMA POWER CO
Qualifying hedges:
Reclassification adjustment for amounts included in net income, tax	0	1
GEORGIA POWER CO
Qualifying hedges:
Reclassification adjustment for amounts included in net income, tax	0	0
MISSISSIPPI POWER CO
Qualifying hedges:
Changes in fair value, tax	0	(1)
SOUTHERN POWER CO
Qualifying hedges:
Changes in fair value, tax	(10)	16
Reclassification adjustment for amounts included in net income, tax	8	(8)
SOUTHERN Co GAS
Qualifying hedges:
Changes in fair value, tax	0	0
Reclassification adjustment for amounts included in net income, tax	0	1
Pension and other postretirement benefit plans:
Reclassification adjustment for amounts included in net income, tax	$ 0	$ 0

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Activities:
Net income (loss)	$ 2,059	$ 936
Adjustments to reconcile net income (loss) to net cash provided from (used for) operating activities —
Depreciation and amortization, total	851	873
Deferred income taxes	191	34
Allowance for equity funds used during construction	(32)	(30)
Pension, postretirement, and other employee benefits	(53)	(27)
Settlement of asset retirement obligations	(62)	(41)
Stock based compensation expense	64	69
Estimated loss on Kemper IGCC	6	37
Mark-to-market adjustments	46	(60)
Gain on dispositions, net	(2,503)	1
Other, net	19	73
Changes in certain current assets and liabilities —
-Receivables	378	197
-Prepayments	(129)	(82)
-Natural gas for sale	363	413
-Other current assets	17	7
-Accounts payable	(783)	(425)
-Accrued taxes	928	(79)
-Accrued compensation	(489)	(471)
-Other current liabilities	(127)	84
Net cash used for operating activities	744	1,509
Investing Activities:
Business acquisitions, net of cash acquired	(2)	(46)
Property additions	(1,678)	(1,781)
Nuclear decommissioning trust fund purchases	(197)	(306)
Nuclear decommissioning trust fund sales	192	301
Cost of removal, net of salvage	(89)	(79)
Proceeds from asset dispositions	4,427	135
Change in construction payables, net	(146)	(112)
Investment in unconsolidated subsidiaries	(10)	(30)
Payments pursuant to LTSAs	(28)	(73)
Other investing activities	(15)	(4)
Net cash provided from (used for) investing activities	2,454	(1,995)
Financing Activities:
Increase (decrease) in notes payable, net	86	782
Proceeds —
Long-term debt	1,220	600
Common stock	224	113
Short-term borrowings	0	1,200
Redemptions and repurchases —
Long-term debt	(2,429)	(1,283)
Short-term borrowings	(1,750)	(150)
Distributions to noncontrolling interests	(36)	(13)
Capital contributions from noncontrolling interests	3	8
Payment of common stock dividends	(623)	(586)
Other financing activities	(48)	(42)
Net cash provided from (used for) financing activities	(3,353)	629
Net Change in Cash, Cash Equivalents, and Restricted Cash	(155)	143
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	1,519	2,147
Cash, Cash Equivalents, and Restricted Cash at End of Period	1,364	2,290
Cash paid (received) during the period for —
Interest, net of amounts capitalized	462	499
Income taxes, net	0	(1)
Noncash transactions — Accrued property additions at end of period	899	894
ALABAMA POWER CO
Operating Activities:
Net income (loss)	221	229
Adjustments to reconcile net income (loss) to net cash provided from (used for) operating activities —
Depreciation and amortization, total	244	228
Deferred income taxes	0	32
Allowance for equity funds used during construction	(14)	(13)
Other, net	(24)	(21)
Changes in certain current assets and liabilities —
-Receivables	105	(1)
-Prepayments	(78)	(82)
-Materials and supplies	(4)	(27)
-Other current assets	19	19
-Accounts payable	(286)	(216)
-Accrued taxes	80	57
-Accrued compensation	(122)	(108)
-Other current liabilities	(9)	45
Net cash used for operating activities	146	155
Investing Activities:
Property additions	(390)	(490)
Nuclear decommissioning trust fund purchases	(68)	(50)
Nuclear decommissioning trust fund sales	68	51
Cost of removal, net of salvage	(16)	(19)
Change in construction payables, net	(95)	(50)
Other investing activities	(10)	(6)
Net cash provided from (used for) investing activities	(511)	(564)
Financing Activities:
Increase (decrease) in notes payable, net	0	245
Proceeds —
Capital contributions from parent company	1,232	484
Redemptions and repurchases —
Senior notes	(200)	0
Payment of common stock dividends	(211)	(202)
Other financing activities	(10)	(9)
Net cash provided from (used for) financing activities	811	518
Net Change in Cash, Cash Equivalents, and Restricted Cash	446	109
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	313	544
Cash, Cash Equivalents, and Restricted Cash at End of Period	759	653
Cash paid (received) during the period for —
Interest, net of amounts capitalized	89	84
Income taxes, net	0	9
Noncash transactions — Accrued property additions at end of period	176	195
GEORGIA POWER CO
Operating Activities:
Net income (loss)	311	352
Adjustments to reconcile net income (loss) to net cash provided from (used for) operating activities —
Depreciation and amortization, total	287	280
Deferred income taxes	127	(38)
Pension, postretirement, and other employee benefits	(35)	(19)
Settlement of asset retirement obligations	(34)	(23)
Other, net	(18)	28
Changes in certain current assets and liabilities —
-Receivables	91	135
-Fossil fuel stock	(41)	24
-Prepaid income taxes	(73)	84
-Other current assets	33	9
-Accounts payable	(166)	(180)
-Accrued taxes	(245)	(191)
-Accrued compensation	(67)	(85)
-Other current liabilities	42	(3)
Net cash used for operating activities	212	373
Investing Activities:
Property additions	(875)	(681)
Nuclear decommissioning trust fund purchases	(129)	(255)
Nuclear decommissioning trust fund sales	124	250
Cost of removal, net of salvage	(58)	(26)
Proceeds from asset dispositions	7	134
Change in construction payables, net of joint owner portion	(38)	(47)
Payments pursuant to LTSAs	(2)	(43)
Other investing activities	(9)	0
Net cash provided from (used for) investing activities	(980)	(668)
Financing Activities:
Increase (decrease) in notes payable, net	(19)	0
Proceeds —
FFB loan	835	0
Pollution control revenue bonds	343	0
Capital contributions from parent company	27	1,474
Redemptions and repurchases —
Pollution control revenue bonds	(108)	(278)
Short-term borrowings	0	(150)
Other long-term debt	0	(100)
Payment of common stock dividends	(394)	(339)
Other financing activities	(19)	(6)
Net cash provided from (used for) financing activities	665	601
Net Change in Cash, Cash Equivalents, and Restricted Cash	(103)	306
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	112	852
Cash, Cash Equivalents, and Restricted Cash at End of Period	9	1,158
Cash paid (received) during the period for —
Interest, net of amounts capitalized	92	115
Noncash transactions — Accrued property additions at end of period	607	525
MISSISSIPPI POWER CO
Operating Activities:
Net income (loss)	37	(7)
Adjustments to reconcile net income (loss) to net cash provided from (used for) operating activities —
Depreciation and amortization, total	50	44
Deferred income taxes	(8)	155
Estimated loss on Kemper IGCC	6	37
Other, net	(10)	3
Changes in certain current assets and liabilities —
-Receivables	11	(129)
-Other current assets	7	(12)
-Accounts payable	(38)	(21)
-Accrued taxes	(62)	(110)
-Accrued compensation	(22)	(22)
-Other current liabilities	6	0
Net cash used for operating activities	(23)	(62)
Investing Activities:
Property additions	(45)	(33)
Change in construction payables, net	(8)	(2)
Other investing activities	(10)	(17)
Net cash provided from (used for) investing activities	(63)	(52)
Financing Activities:
Increase (decrease) in notes payable, net	0	(4)
Proceeds —
Senior notes	0	600
Short-term borrowings	0	300
Pollution control revenue bonds	43	0
Redemptions and repurchases —
Other long-term debt	0	(900)
Return of capital	(38)	0
Other financing activities	0	(5)
Net cash provided from (used for) financing activities	5	(9)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(81)	(123)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	293	248
Cash, Cash Equivalents, and Restricted Cash at End of Period	212	125
Cash paid (received) during the period for —
Interest, net of amounts capitalized	13	21
Income taxes, net	0	19
Noncash transactions — Accrued property additions at end of period	27	30
SOUTHERN POWER CO
Operating Activities:
Net income (loss)	27	115
Adjustments to reconcile net income (loss) to net cash provided from (used for) operating activities —
Depreciation and amortization, total	125	122
Deferred income taxes	17	(50)
Amortization of investment tax credits	(14)	(14)
Other, net	(7)	2
Changes in certain current assets and liabilities —
-Receivables	10	48
-Prepaid income taxes	(9)	(32)
-Other current assets	3	5
-Accounts payable	(32)	(43)
-Accrued compensation	(15)	(13)
-Other current liabilities	5	9
Net cash used for operating activities	110	149
Investing Activities:
Business acquisitions, net of cash acquired	(2)	(46)
Property additions	(66)	(121)
Change in construction payables, net	(7)	25
Payments pursuant to LTSAs	(15)	(18)
Other investing activities	11	7
Net cash provided from (used for) investing activities	(79)	(153)
Financing Activities:
Increase (decrease) in notes payable, net	5	29
Redemptions and repurchases —
Distributions to noncontrolling interests	(36)	(13)
Capital contributions from noncontrolling interests	3	8
Payment of common stock dividends	(51)	(78)
Net cash provided from (used for) financing activities	(79)	(54)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(48)	(58)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	181	140
Cash, Cash Equivalents, and Restricted Cash at End of Period	133	82
Cash paid (received) during the period for —
Interest, net of amounts capitalized	28	29
Income taxes, net	1	(39)
Noncash transactions — Accrued property additions at end of period	19	57
SOUTHERN Co GAS
Operating Activities:
Net income (loss)	270	279
Adjustments to reconcile net income (loss) to net cash provided from (used for) operating activities —
Depreciation and amortization, total	118	129
Deferred income taxes	42	47
Mark-to-market adjustments	45	(59)
Goodwill impairment	0	42
Other, net	(20)	(2)
Changes in certain current assets and liabilities —
-Receivables	238	175
-Natural gas for sale	363	413
-Other current assets	59	35
-Accounts payable	(353)	(119)
-Accrued taxes	21	28
-Accrued compensation	(50)	(38)
-Other current liabilities	(50)	48
Net cash used for operating activities	683	978
Investing Activities:
Property additions	(256)	(268)
Cost of removal, net of salvage	(12)	(14)
Change in construction payables, net	1	(46)
Investment in unconsolidated subsidiaries	(10)	(29)
Other investing activities	(13)	(4)
Net cash provided from (used for) investing activities	(290)	(361)
Financing Activities:
Increase (decrease) in notes payable, net	(289)	(483)
Redemptions and repurchases —
Payment of common stock dividends	(118)	(118)
Other financing activities	5	6
Net cash provided from (used for) financing activities	(402)	(595)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(9)	22
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	70	78
Cash, Cash Equivalents, and Restricted Cash at End of Period	61	100
Cash paid (received) during the period for —
Interest, net of amounts capitalized	55	52
Income taxes, net	(1)	0
Noncash transactions — Accrued property additions at end of period	$ 98	$ 89

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest capitalized	$ 18	$ 17
ALABAMA POWER CO
Interest capitalized	5	5
GEORGIA POWER CO
Interest capitalized	8	6
MISSISSIPPI POWER CO
Interest capitalized	0	0
SOUTHERN POWER CO
Interest capitalized	4	5
SOUTHERN Co GAS
Interest capitalized	$ 2	$ 1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 1,361	$ 1,396
Receivables —
Customer accounts receivable	1,715	1,726
Energy marketing receivables	529	801
Unbilled revenues	555	654
Under recovered fuel clause revenues	73	115
Other accounts and notes receivable	863	813
Accumulated provision for uncollectible accounts	(46)	(50)
Materials and supplies	1,477	1,465
Fossil fuel for generation	427	405
Natural gas for sale	189	524
Prepaid expenses	786	432
Assets from risk management activities, net of collateral	111	222
Other regulatory assets	482	525
Assets held for sale	55	393
Other current assets	132	162
Total current assets	8,709	9,583
Property, Plant, and Equipment:
In service	102,673	103,706
Less: Accumulated depreciation	30,834	31,038
Plant in service, net of depreciation	71,839	72,668
Other utility plant, net	1,315	0
Nuclear fuel, at amortized cost	885	875
Construction work in progress	7,598	7,254
Total property, plant, and equipment	81,637	80,797
Other Property and Investments:
Goodwill	5,284	5,315
Equity investments in unconsolidated subsidiaries	1,598	1,580
Other intangible assets, net of amortization	585	613
Nuclear decommissioning trusts, at fair value	1,875	1,721
Leveraged leases	806	798
Miscellaneous property and investments	363	269
Total other property and investments	10,511	10,296
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,881
Deferred charges related to income taxes	794	794
Unamortized loss on reacquired debt	318	323
Other regulatory assets, deferred	8,191	8,308
Assets held for sale, deferred	763	5,350
Other deferred charges and assets	1,292	1,463
Total deferred charges and other assets	13,239	16,238
Total Assets	114,096	116,914
Current Liabilities:
Securities due within one year	2,315	3,198
Notes payable	1,251	2,915
Energy marketing trade payables	532	856
Accounts payable —
Accounts payable	2,037	2,580
Customer deposits	483	522
Accrued taxes —
Accrued income taxes	340	21
Other accrued taxes	331	635
Accrued interest	412	472
Accrued compensation	473	1,030
Asset retirement obligations	417	404
Other regulatory liabilities	310	376
Liabilities held for sale	38	425
Operating lease obligations	226
Other current liabilities	754	852
Total current liabilities	9,919	14,286
Long-term Debt	40,457	40,736
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	7,937	6,558
Deferred credits related to income taxes	6,417	6,460
Accumulated deferred ITCs	2,353	2,372
Employee benefit obligations	2,084	2,147
Operating lease obligations, deferred	1,720
Asset retirement obligations, deferred	9,011	8,990
Accrued environmental remediation	261	268
Other cost of removal obligations	2,304	2,297
Other regulatory liabilities, deferred	211	169
Liabilities held for sale, deferred	39	2,836
Other deferred credits and liabilities	405	465
Total deferred credits and other liabilities	32,742	32,562
Total Liabilities	83,118	87,584
Redeemable Preferred Stock of Subsidiaries	291	291
Stockholders' Equity:
Total stockholders' equity	30,687	29,039
Total Liabilities and Stockholders' Equity	114,096	116,914
ALABAMA POWER CO
Current Assets:
Cash and cash equivalents	759	313
Receivables —
Customer accounts receivable	382	403
Unbilled revenues	126	150
Affiliated	45	94
Other accounts and notes receivable	58	51
Accumulated provision for uncollectible accounts	(10)	(10)
Materials and supplies	558	546
Fossil fuel for generation	120	141
Prepaid expenses	113	66
Other regulatory assets	125	137
Other current assets	21	18
Total current assets	2,297	1,909
Property, Plant, and Equipment:
In service	28,810	30,402
Less: Accumulated depreciation	9,447	9,988
Plant in service, net of depreciation	19,363	20,414
Other utility plant, net	1,315	0
Nuclear fuel, at amortized cost	320	324
Construction work in progress	1,023	1,113
Total property, plant, and equipment	22,021	21,851
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	64	65
Nuclear decommissioning trusts, at fair value	933	847
Miscellaneous property and investments	129	127
Total other property and investments	1,126	1,039
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	160
Deferred charges related to income taxes	239	240
Deferred under recovered regulatory clause revenues	21	116
Other regulatory assets, deferred	1,350	1,386
Other deferred charges and assets	193	189
Total deferred charges and other assets	1,963	1,931
Total Assets	27,407	26,730
Current Liabilities:
Securities due within one year	1	201
Accounts payable —
Affiliated	262	364
Other	346	614
Customer deposits	97	96
Accrued taxes —
Other accrued taxes	97	44
Accrued interest	77	89
Accrued compensation	102	227
Asset retirement obligations	163	163
Operating lease obligations	47
Other current liabilities	97	161
Total current liabilities	1,242	1,959
Long-term Debt	7,924	7,923
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	2,971	2,962
Deferred credits related to income taxes	2,015	2,027
Accumulated deferred ITCs	105	106
Employee benefit obligations	302	314
Operating lease obligations, deferred	147
Asset retirement obligations, deferred	3,064	3,047
Other cost of removal obligations	489	497
Other regulatory liabilities, deferred	107	69
Other deferred credits and liabilities	30	58
Total deferred credits and other liabilities	9,230	9,080
Total Liabilities	18,396	18,962
Redeemable Preferred Stock	291	291
Stockholders' Equity:
Total stockholders' equity	8,720	7,477
Total Liabilities and Stockholders' Equity	27,407	26,730
GEORGIA POWER CO
Current Assets:
Cash and cash equivalents	9	4
Restricted cash and cash equivalents	0	108
Receivables —
Customer accounts receivable	550	591
Unbilled revenues	179	208
Under recovered fuel clause revenues	73	115
Joint owner accounts receivable	170	170
Affiliated	21	39
Other accounts and notes receivable	241	80
Accumulated provision for uncollectible accounts	(2)	(2)
Materials and supplies	504	519
Fossil fuel for generation	272	231
Prepaid expenses	193	142
Other regulatory assets	210	199
Other current assets	48	70
Total current assets	2,468	2,474
Property, Plant, and Equipment:
In service	38,015	37,675
Less: Accumulated depreciation	12,210	12,096
Plant in service, net of depreciation	25,805	25,579
Nuclear fuel, at amortized cost	565	550
Construction work in progress	5,298	4,833
Total property, plant, and equipment	31,668	30,962
Other Property and Investments:
Equity investments in unconsolidated subsidiaries	50	51
Nuclear decommissioning trusts, at fair value	942	873
Miscellaneous property and investments	73	72
Total other property and investments	1,065	996
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	1,519
Deferred charges related to income taxes	518	517
Other regulatory assets, deferred	4,921	4,902
Other deferred charges and assets	379	514
Total deferred charges and other assets	7,337	5,933
Total Assets	42,538	40,365
Current Liabilities:
Securities due within one year	973	617
Notes payable	275	294
Accounts payable —
Affiliated	448	575
Other	827	890
Customer deposits	278	276
Accrued taxes —
Other accrued taxes	132	377
Accrued interest	103	105
Accrued compensation	112	221
Asset retirement obligations	221	202
Other regulatory liabilities	197	169
Operating lease obligations	139
Other current liabilities	305	183
Total current liabilities	3,871	3,909
Long-term Debt	10,108	9,364
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	3,192	3,062
Deferred credits related to income taxes	3,079	3,080
Accumulated deferred ITCs	259	262
Employee benefit obligations	567	599
Operating lease obligations, deferred	1,404
Asset retirement obligations, deferred	5,634	5,627
Other deferred credits and liabilities	155	139
Total deferred credits and other liabilities	14,290	12,769
Total Liabilities	28,269	26,042
Stockholders' Equity:
Total stockholders' equity	14,269	14,323
Total Liabilities and Stockholders' Equity	42,538	40,365
MISSISSIPPI POWER CO
Current Assets:
Cash and cash equivalents	212	293
Receivables —
Customer accounts receivable	29	34
Unbilled revenues	37	41
Affiliated	16	21
Other accounts and notes receivable	36	31
Materials and supplies	52	53
Fossil fuel for generation	23	20
Other regulatory assets	102	116
Other current assets	6	19
Total current assets	513	628
Property, Plant, and Equipment:
In service	4,821	4,900
Less: Accumulated depreciation	1,467	1,429
Plant in service, net of depreciation	3,354	3,471
Construction work in progress	110	103
Total property, plant, and equipment	3,464	3,574
Other Property and Investments:
Total other property and investments	123	24
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	8
Deferred charges related to income taxes	33	33
Other regulatory assets, deferred	487	474
Accumulated deferred income taxes	148	150
Other deferred charges and assets	17	3
Total deferred charges and other assets	685	660
Total Assets	4,785	4,886
Current Liabilities:
Securities due within one year	339	40
Accounts payable —
Affiliated	52	60
Other	50	90
Accrued taxes —
Other accrued taxes	33	95
Accrued interest	20	15
Accrued compensation	16	38
Accrued plant closure costs	26	29
Asset retirement obligations	28	34
Operating lease obligations	3
Other current liabilities	55	40
Over recovered regulatory clause liabilities	14	14
Total current liabilities	633	455
Long-term Debt	1,280	1,539
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	373	378
Deferred credits related to income taxes	367	382
Employee benefit obligations	111	115
Operating lease obligations, deferred	5
Asset retirement obligations, deferred	127	126
Other cost of removal obligations	186	185
Other regulatory liabilities, deferred	80	81
Other deferred credits and liabilities	18	16
Total deferred credits and other liabilities	1,262	1,283
Total Liabilities	3,175	3,277
Stockholders' Equity:
Total stockholders' equity	1,610	1,609
Total Liabilities and Stockholders' Equity	4,785	4,886
SOUTHERN POWER CO
Current Assets:
Cash and cash equivalents	133	181
Receivables —
Customer accounts receivable	120	111
Affiliated	33	55
Other accounts and notes receivable	116	116
Materials and supplies	218	220
Prepaid income taxes	1,190	25
Other current assets	37	37
Total current assets	1,847	745
Property, Plant, and Equipment:
In service	13,284	13,271
Less: Accumulated depreciation	2,288	2,171
Plant in service, net of depreciation	10,996	11,100
Construction work in progress	409	430
Total property, plant, and equipment	11,405	11,530
Other Property and Investments:
Intangible assets, net of amortization	340	345
Miscellaneous property and investments	2	0
Total other property and investments	342	345
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	372
Prepaid LTSAs	102	98
Accumulated deferred income taxes	17	1,186
Income taxes receivable, non-current	33	30
Assets held for sale, deferred	644	576
Other deferred charges and assets	342	373
Total deferred charges and other assets	1,510	2,263
Total Assets	15,104	14,883
Current Liabilities:
Securities due within one year	599	599
Notes payable	105	100
Accounts payable —
Affiliated	69	92
Other	66	77
Accrued taxes —
Accrued income taxes	11	6
Accrued interest	44	36
Liabilities held for sale	9	15
Operating lease obligations	22
Other current liabilities	111	106
Total current liabilities	1,014	1,031
Long-term Debt	4,396	4,418
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	107	105
Accumulated deferred ITCs	1,817	1,832
Operating lease obligations, deferred	371
Other deferred credits and liabilities	181	213
Total deferred credits and other liabilities	2,476	2,150
Total Liabilities	7,886	7,599
Stockholders' Equity:
Total stockholders' equity	7,218	7,284
Total Liabilities and Stockholders' Equity	15,104	14,883
SOUTHERN Co GAS
Current Assets:
Cash and cash equivalents	57	64
Receivables —
Customer accounts receivable	472	370
Energy marketing receivables	529	801
Unbilled revenues	179	213
Affiliated	9	11
Other accounts and notes receivable	108	142
Accumulated provision for uncollectible accounts	(27)	(30)
Natural gas for sale	189	524
Prepaid expenses	99	118
Assets from risk management activities, net of collateral	108	219
Other regulatory assets	46	73
Other current assets	42	50
Total current assets	1,811	2,555
Property, Plant, and Equipment:
In service	15,417	15,177
Less: Accumulated depreciation	4,466	4,400
Plant in service, net of depreciation	10,951	10,777
Construction work in progress	577	580
Total property, plant, and equipment	11,528	11,357
Other Property and Investments:
Goodwill	5,015	5,015
Equity investments in unconsolidated subsidiaries	1,557	1,538
Other intangible assets, net of amortization	93	101
Miscellaneous property and investments	20	20
Total other property and investments	6,685	6,674
Deferred Charges and Other Assets:
Operating lease right-of-use assets, net of amortization	86
Other regulatory assets, deferred	657	669
Other deferred charges and assets	185	193
Total deferred charges and other assets	928	862
Total Assets	20,952	21,448
Current Liabilities:
Securities due within one year	354	357
Notes payable	361	650
Energy marketing trade payables	532	856
Accounts payable —
Affiliated	31	45
Other	391	402
Customer deposits	91	133
Accrued taxes —
Accrued income taxes	89	66
Other accrued taxes	72	75
Accrued interest	64	55
Accrued compensation	49	100
Liabilities from risk management activities, net of collateral	26	76
Other regulatory liabilities	86	79
Operating lease obligations	13
Other current liabilities	160	130
Total current liabilities	2,306	3,024
Long-term Debt	5,574	5,583
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,064	1,016
Deferred credits related to income taxes	926	940
Employee benefit obligations	351	357
Operating lease obligations, deferred	71
Accrued environmental remediation	261	268
Other cost of removal obligations	1,598	1,585
Other deferred credits and liabilities	63	105
Total deferred credits and other liabilities	4,334	4,271
Total Liabilities	12,214	12,878
Stockholders' Equity:
Total stockholders' equity	8,738	8,570
Total Liabilities and Stockholders' Equity	$ 20,952	$ 21,448

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Other intangible assets, amortization	$ 251	$ 235
SOUTHERN POWER CO
Other intangible assets, amortization	67	61
SOUTHERN Co GAS
Other intangible assets, amortization	$ 153	$ 145

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Treasury	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	ALABAMA POWER CO	ALABAMA POWER COCommon Stock	ALABAMA POWER COPaid-In Capital	ALABAMA POWER CORetained Earnings	ALABAMA POWER COAccumulated Other Comprehensive Income (Loss)	GEORGIA POWER CO	GEORGIA POWER COCommon Stock	GEORGIA POWER COPaid-In Capital	GEORGIA POWER CORetained Earnings	GEORGIA POWER COAccumulated Other Comprehensive Income (Loss)	MISSISSIPPI POWER CO	MISSISSIPPI POWER COCommon Stock	MISSISSIPPI POWER COPaid-In Capital	MISSISSIPPI POWER CORetained Earnings	MISSISSIPPI POWER COAccumulated Other Comprehensive Income (Loss)	SOUTHERN POWER CO	SOUTHERN POWER COPaid-In Capital	SOUTHERN POWER CORetained Earnings	SOUTHERN POWER COAccumulated Other Comprehensive Income (Loss)	SOUTHERN POWER COTotal Common Stockholders' Equity	SOUTHERN POWER CONoncontrolling Interests	SOUTHERN Co GAS	SOUTHERN Co GASPaid-In Capital	SOUTHERN Co GASRetained Earnings	SOUTHERN Co GASAccumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		1,008,532	929						31,000					9,000					1,000
Beginning balance at Dec. 31, 2017	$ 25,528	$ 5,037	$ (36)	$ 10,470	$ 8,885	$ (189)	$ 1,361	$ 6,829	$ 1,222	$ 2,986	$ 2,647	$ (26)	$ 11,931	$ 398	$ 7,328	$ 4,215	$ (10)	$ 1,358	$ 38	$ 4,529	$ (3,205)	$ (4)	$ 6,498	$ 3,662	$ 1,478	$ (2)	$ 5,138	$ 1,360	$ 9,022	$ 9,214	$ (212)	$ 20
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	938				938			225			225		352			352		(7)			(7)		121		121		121		279		279
Other comprehensive income (loss)	30					30		1				1	1				1	(1)				(1)	24			24	24		2			2
Stock issued (in shares)		4,055
Stock issued	113	$ 16		97
Stock-based compensation	36			36
Cash dividends on common stock	(586)				(586)			(202)			(202)		(339)			(339)							(78)		(78)		(78)		(118)		(118)
Contributions from noncontrolling interests	9						9																9					9
Distributions to noncontrolling interests	(13)						(13)																(13)					(13)
Net income (loss) attributable to noncontrolling interests	(6)						(6)																(6)					(6)
Other (in shares)			(33)
Other	(24)	$ 1	$ (2)		20	(41)	(2)	(6)				(6)	(1)		1		(2)	(1)			(1)		2		(2)	5	3	(1)	0		(4)	4
Return of capital																		0
Capital contributions from parent company								488		488			1,476		1,476			2		2			1	1			1		14	14
Ending balance (in shares) at Mar. 31, 2018		1,012,587	962						31,000					9,000					1,000
Ending balance at Mar. 31, 2018	26,025	$ 5,054	$ (38)	10,603	9,257	(200)	1,349	7,335	$ 1,222	3,474	2,670	(31)	13,420	$ 398	8,805	4,228	(11)	1,351	$ 38	4,531	(3,213)	(5)	6,558	3,663	1,519	27	5,209	1,349	9,199	9,228	(55)	26
Beginning balance (in shares) at Dec. 31, 2018		1,034,741	953						31,000					9,000					1,000
Beginning balance at Dec. 31, 2018	29,039	$ 5,164	$ (38)	11,094	8,706	(203)	4,316	7,477	$ 1,222	3,508	2,775	(28)	14,323	$ 398	10,322	3,612	(9)	1,609	$ 38	4,546	(2,971)	(4)	7,284	1,600	1,352	16	2,968	4,316	8,570	8,856	(312)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,084				2,084			217			217		311			311		37			37		56		56		56		270		270
Other comprehensive income (loss)								1				1	1				1						(4)			(4)	(4)		(1)			(1)
Stock issued (in shares)		6,547
Stock issued	224	$ 28		196
Stock-based compensation	24			24
Cash dividends on common stock	(622)				(622)			(211)			(211)		(394)			(394)							(51)		(51)		(51)		(118)		(118)
Contributions from noncontrolling interests	3						3																3					3
Distributions to noncontrolling interests	(41)						(41)																(41)					(41)
Net income (loss) attributable to noncontrolling interests	(29)						(29)																(29)					(29)
Other (in shares)			(39)
Other	5		$ (2)	7	(1)		1						(1)		(1)		0						(1)	(1)	(1)		(2)	1
Return of capital																		(38)		(38)
Capital contributions from parent company								1,236		1,236			29		29			2		2			1	1			1		17	17
Ending balance (in shares) at Mar. 31, 2019		1,041,288	992						31,000					9,000					1,000
Ending balance at Mar. 31, 2019	$ 30,687	$ 5,192	$ (40)	$ 11,321	$ 10,167	$ (203)	$ 4,250	$ 8,720	$ 1,222	$ 4,744	$ 2,781	$ (27)	$ 14,269	$ 398	$ 10,350	$ 3,529	$ (8)	$ 1,610	$ 38	$ 4,510	$ (2,934)	$ (4)	$ 7,218	$ 1,600	$ 1,356	$ 12	$ 2,968	$ 4,250	$ 8,738	$ 8,873	$ (160)	$ 25

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Cash dividends (in dollars per share)	$ 0.60	$ 0.58

Introduction

Introduction	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
INTRODUCTION	INTRODUCTION The condensed quarterly financial statements of each registrant included herein have been prepared by such registrant, without audit, pursuant to the rules and regulations of the SEC. The Condensed Balance Sheets as of December 31, 2018 have been derived from the audited financial statements of each registrant. In the opinion of each registrant's management, the information regarding such registrant furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended March 31, 2019 and 2018 . Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although each registrant believes that the disclosures regarding such registrant are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for energy, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year. Certain prior year data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the results of operations, financial position, or cash flows of any registrant. Recently Adopted Accounting Standards In 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changes the recognition, measurement, and presentation of expense associated with leases and provides clarification regarding the identification of certain components of contracts that would represent a lease. The accounting required by lessors is relatively unchanged and there is no change to the accounting for existing leveraged leases. The registrants adopted the new standard effective January 1, 2019. See Note (L) for additional information and related disclosures. Goodwill and Other Intangible Assets Goodwill at March 31, 2019 and December 31, 2018 was as follows: At March 31, 2019 At December 31, 2018 (in millions) Southern Company $ 5,284 $ 5,315 Southern Company Gas: Gas distribution operations $ 4,034 $ 4,034 Gas marketing services 981 981 Southern Company Gas total $ 5,015 $ 5,015 Goodwill is not amortized but is subject to an annual impairment test during the fourth quarter of each year or more frequently if impairment indicators arise. Other intangible assets were as follows: At March 31, 2019 At December 31, 2018 Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 211 $ (100 ) $ 111 $ 223 $ (94 ) $ 129 Trade names 70 (22 ) 48 70 (21 ) 49 Storage and transportation contracts 64 (56 ) 8 64 (54 ) 10 PPA fair value adjustments 405 (67 ) 338 405 (61 ) 344 Other 11 (6 ) 5 11 (5 ) 6 Total other intangible assets subject to amortization $ 761 $ (251 ) $ 510 $ 773 $ (235 ) $ 538 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 836 $ (251 ) $ 585 $ 848 $ (235 ) $ 613 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 405 $ (67 ) $ 338 $ 405 $ (61 ) $ 344 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (89 ) $ 67 $ 156 $ (84 ) $ 72 Trade names 26 (8 ) 18 26 (7 ) 19 Wholesale gas services Storage and transportation contracts 64 (56 ) 8 64 (54 ) 10 Total other intangible assets subject to amortization $ 246 $ (153 ) $ 93 $ 246 $ (145 ) $ 101 Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2019 (in millions) Southern Company $ 17 Southern Power (a) $ 6 Southern Company Gas Gas marketing services (b) $ 6 Wholesale gas services (a) 2 Southern Company Gas total $ 8 (a) Recorded as a reduction to operating revenues. (b) Included in depreciation and amortization. Restricted Cash At December 31, 2018, Georgia Power had restricted cash related to the redemption of pollution control revenue bonds, which were redeemed in January 2019. See Note (F) under " Financing Activities " for additional information. At both March 31, 2019 and December 31, 2018 , Southern Company Gas had restricted cash held as collateral for worker's compensation, life insurance, and long-term disability insurance. The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amounts shown in the condensed statements of cash flows for the registrants that had restricted cash at March 31, 2019 and/or December 31, 2018 : Southern Company Southern Company Gas (in millions) At March 31, 2019 Cash and cash equivalents $ 1,361 $ 57 Restricted cash: Other accounts and notes receivable 4 4 Total cash, cash equivalents, and restricted cash $ 1,364 (*) $ 61 (*) Total does not add due to rounding. 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 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 Natural Gas for Sale Southern Company Gas, with the exception of Nicor Gas, carries natural gas inventory on a WACOG basis. For any declines in market prices below the WACOG considered to be other than temporary, an adjustment is recorded to reduce the value of natural gas inventories to market value. Southern Company Gas had no material adjustment in any period presented. 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. Nicor Gas' inventory decrement at March 31, 2019 is expected to be restored prior to year end.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
REGULATORY MATTERS	REGULATORY MATTERS See Note 2 to the financial statements in Item 8 of the Form 10-K for additional information relating to regulatory matters. The recovery balances for certain of Alabama Power's, Georgia Power's, and Mississippi Power's regulatory clauses at March 31, 2019 and December 31, 2018 were as follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, (in millions) Alabama Power Rate CNP Compliance Deferred under recovered regulatory clause revenues $ — $ 42 Customer accounts receivable 25 — Rate CNP PPA Deferred under recovered regulatory clause revenues 21 25 Retail Energy Cost Recovery (*) Deferred under recovered regulatory clause revenues — 109 Other regulatory liabilities, deferred 2 — Natural Disaster Reserve Other regulatory liabilities, deferred 22 20 Georgia Power Fuel Cost Recovery Receivables – under recovered fuel clause revenues $ 73 $ 115 Mississippi Power Fuel Cost Recovery Over recovered retail fuel costs $ 10 $ 8 (*) In accordance with an accounting order issued on February 5, 2019 by the Alabama PSC, Alabama Power utilized $75 million of the 2018 Rate RSE refund liability to reduce the Rate ECR under recovered balance. See Note 2 to the financial statements under "Alabama Power – Rate ECR" in Item 8 of the Form 10-K for additional information. Alabama Power Environmental Accounting Order In connection with management's decision to retire Plant Gorgas, in February 2019, Alabama Power reclassified approximately $1.3 billion for Plant Gorgas Unit 10 from plant in service, net of depreciation to other utility plant, net and continued to depreciate the asset according to the original depreciation rates. On April 15, 2019, Alabama Power retired Plant Gorgas Units 8, 9, and 10 and reclassified approximately $740 million of the remaining net investment costs of the units to a regulatory asset to be recovered over the units' remaining useful lives as established prior to the decision to retire. Additionally, approximately $700 million of net capitalized asset retirement costs will be reclassified to a regulatory asset and recovered in accordance with accounting guidance provided by the Alabama PSC. See Note 2 to the financial statements under "Alabama Power – Environmental Accounting Order" and Note 6 in Item 8 of the Form 10-K for additional information. Georgia Power Nuclear Construction See Note 2 to the financial statements under "Georgia Power – Nuclear Construction" in Item 8 of the Form 10-K for additional information regarding Georgia Power's construction of Plant Vogtle Units 3 and 4, the joint ownership agreements and related funding agreement, VCM reports, and the NCCR tariff. In 2009, the Georgia PSC certified construction of Plant Vogtle Units 3 and 4. Georgia Power holds a 45.7% ownership interest in Plant Vogtle Units 3 and 4. In 2012, the NRC issued the related combined construction and operating licenses, which allowed full construction of the two AP1000 nuclear units (with electric generating capacity of approximately 1,100 MWs each) and related facilities to begin. Until March 2017, construction on Plant Vogtle Units 3 and 4 continued under the Vogtle 3 and 4 Agreement, which was a substantially fixed price agreement. In March 2017, the EPC Contractor filed for bankruptcy protection under Chapter 11 of the U.S. Bankruptcy Code. In connection with the EPC Contractor's bankruptcy filing, Georgia Power, acting for itself and as agent for the other Vogtle Owners, entered into several transitional arrangements to allow construction to continue. In July 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, entered into the Vogtle Services Agreement, whereby Westinghouse provides facility design and engineering services, procurement and technical support, and staff augmentation on a time and materials cost basis. The Vogtle Services Agreement provides that it will continue until the start-up and testing of Plant Vogtle Units 3 and 4 are complete and electricity is generated and sold from both units. The Vogtle Services Agreement is terminable by the Vogtle Owners upon 30 days' written notice. In October 2017, Georgia Power, acting for itself and as agent for the other Vogtle Owners, executed the Bechtel Agreement, a cost reimbursable plus fee arrangement, whereby Bechtel is reimbursed for actual costs plus a base fee and an at-risk fee, which is subject to adjustment based on Bechtel's performance against cost and schedule targets. Each Vogtle Owner is severally (not jointly) liable for its proportionate share, based on its ownership interest, of all amounts owed to Bechtel under the Bechtel Agreement. The Vogtle Owners may terminate the Bechtel Agreement at any time for their convenience, provided that the Vogtle Owners will be required to pay amounts related to work performed prior to the termination (including the applicable portion of the base fee), certain termination-related costs, and, at certain stages of the work, the applicable portion of the at-risk fee. Bechtel may terminate the Bechtel Agreement under certain circumstances, including certain Vogtle Owner suspensions of work, certain breaches of the Bechtel Agreement by the Vogtle Owners, Vogtle Owner insolvency, and certain other events. 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 March 31, 2019 (b) (4.9 ) Remaining estimate to complete (a) $ 3.5 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $325 million . (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related Customer Refunds. Georgia Power estimates that its financing costs for construction of Plant Vogtle Units 3 and 4 will total approximately $3.1 billion , of which $1.9 billion had been incurred through March 31, 2019 . In April 2019, Southern Nuclear completed a cost and schedule validation process to verify and update quantities of commodities remaining to install, labor hours to install remaining quantities and related productivity, testing and system turnover requirements, and forecasted staffing needs and related costs. This process confirmed the total estimated project capital cost forecast for Plant Vogtle Units 3 and 4. The expected in-service dates of November 2021 for Unit 3 and November 2022 for Unit 4, as previously approved by the Georgia PSC, remain unchanged. As construction continues, challenges with management of contractors, subcontractors, and vendors; supervision of craft labor and related craft labor productivity, ability to attract and retain craft labor, and/or related cost escalation; procurement, fabrication, delivery, assembly, and/or installation and the initial testing and start-up, including any required engineering changes, of plant systems, structures, or components (some of which are based on new technology that only recently began initial operation in the global nuclear industry at this scale), any of which may require additional labor and/or materials; or other issues could arise and change the projected schedule and estimated cost. Monthly construction production targets established as part of a strategy to maintain and build margin to the approved in-service dates will continue to increase significantly throughout 2019. To meet these increasing monthly targets, existing craft construction productivity must improve and additional craft laborers must be retained and deployed. There have been technical and procedural challenges to the construction and licensing of Plant Vogtle Units 3 and 4 at the federal and state level and additional challenges may arise. Processes are in place that are designed to assure compliance with the requirements specified in the Westinghouse Design Control Document and the combined construction and operating licenses, including inspections by Southern Nuclear and the NRC that occur throughout construction. As a result of such compliance processes, certain license amendment requests have been filed and approved or are pending before the NRC. Various design and other licensing-based compliance matters, including the timely resolution of ITAAC and the related approvals by the NRC, may arise, which may result in additional license amendments or require other resolution. If any license amendment requests or other licensing-based compliance issues are not resolved in a timely manner, there may be delays in the project schedule that could result in increased costs. The ultimate outcome of these matters cannot be determined at this time. However, any extension of the regulatory-approved project schedule is currently estimated to result in additional base capital costs of approximately $50 million per month, based on Georgia Power's ownership interests, and AFUDC of approximately $12 million per month. While Georgia Power is not precluded from seeking recovery of any future capital cost forecast increase, management will ultimately determine whether or not to seek recovery. Any further changes to the capital cost forecast that are not expected to be recoverable through regulated rates will be required to be charged to income and such charges could be material. Joint Owner Contracts In November 2017, the Vogtle Owners entered into an amendment to their joint ownership agreements for Plant Vogtle Units 3 and 4 to provide for, among other conditions, additional Vogtle Owner approval requirements. Effective in August 2018, the Vogtle Owners further amended the joint ownership agreements to clarify and provide procedures for certain provisions of the joint ownership agreements related to adverse events that require the vote of the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 to continue construction (as amended, and together with the November 2017 amendment, the Vogtle Joint Ownership Agreements). The Vogtle Joint Ownership Agreements also confirm that the Vogtle Owners' sole recourse against Georgia Power or Southern Nuclear for any action or inaction in connection with their performance as agent for the Vogtle Owners is limited to removal of Georgia Power and/or Southern Nuclear as agent, except in cases of willful misconduct. As a result of the increase in the total project capital cost forecast and Georgia Power's decision not to seek rate recovery of the increase in the base capital costs in conjunction with the nineteenth VCM report, the holders of at least 90% of the ownership interests in Plant Vogtle Units 3 and 4 were required to vote to continue construction. In September 2018, the Vogtle Owners unanimously voted to continue construction of Plant Vogtle Units 3 and 4. Amendments to the Vogtle Joint Ownership Agreements In connection with the vote to continue construction, Georgia Power entered into (i) a binding term sheet (Vogtle Owner Term Sheet) with the other Vogtle Owners and MEAG's wholly-owned subsidiaries MEAG Power SPVJ, LLC (MEAG SPVJ), MEAG Power SPVM, LLC (MEAG SPVM), and MEAG Power SPVP, LLC (MEAG SPVP) to take certain actions which partially mitigate potential financial exposure for the other Vogtle Owners, including additional amendments to the Vogtle Joint Ownership Agreements and the purchase of PTCs from the other Vogtle Owners at pre-established prices, and (ii) a term sheet (MEAG Term Sheet) with MEAG and MEAG SPVJ to provide funding with respect to MEAG SPVJ's ownership interest in Plant Vogtle Units 3 and 4 under certain circumstances. On January 14, 2019, Georgia Power, MEAG, and MEAG SPVJ entered into an agreement to implement the provisions of the MEAG Term Sheet. On February 18, 2019, Georgia Power, the other Vogtle Owners, and MEAG's wholly-owned subsidiaries MEAG SPVJ, MEAG SPVM, and MEAG SPVP entered into certain amendments to the Vogtle Joint Ownership Agreements to implement the provisions of the Vogtle Owner Term Sheet. The ultimate outcome of these matters cannot be determined at this time. Regulatory Matters In 2009, the Georgia PSC voted to certify construction of Plant Vogtle Units 3 and 4 with a certified capital cost of $4.418 billion . In addition, in 2009 the Georgia PSC approved inclusion of the Plant Vogtle Units 3 and 4 related CWIP accounts in rate base, and the State of Georgia enacted the Georgia Nuclear Energy Financing Act, which allows Georgia Power to recover financing costs for Plant Vogtle Units 3 and 4. Financing costs are recovered on all applicable certified costs through annual adjustments to the NCCR tariff up to the certified capital cost of $4.418 billion . At March 31, 2019 , Georgia Power had recovered approximately $1.9 billion of financing costs. Financing costs related to capital costs above $4.418 billion will be recovered through AFUDC; however, Georgia Power will not record AFUDC related to any capital costs in excess of the total deemed reasonable by the Georgia PSC (currently $7.3 billion ) and not requested for rate recovery. In December 2018, the Georgia PSC approved Georgia Power's request to increase the NCCR tariff by $88 million annually, effective January 1, 2019. Georgia Power is required to file semi-annual VCM reports with the Georgia PSC by February 28 and August 31 of each year. In 2013, in connection with the eighth VCM report, the Georgia PSC approved a stipulation between Georgia Power and the staff of the Georgia PSC to waive the requirement to amend the Plant Vogtle Units 3 and 4 certificate in accordance with the 2009 certification order until the completion of Plant Vogtle Unit 3, or earlier if deemed appropriate by the Georgia PSC and Georgia Power. In 2016, the Georgia PSC voted to approve a settlement agreement (Vogtle Cost Settlement Agreement) resolving certain prudency matters in connection with the fifteenth VCM report. In December 2017, the Georgia PSC voted to approve (and issued its related order on January 11, 2018) Georgia Power's seventeenth VCM report and modified the Vogtle Cost Settlement Agreement. The Vogtle Cost Settlement Agreement, as modified by the January 11, 2018 order, resolved the following regulatory matters related to Plant Vogtle Units 3 and 4: (i) none of the $3.3 billion of costs incurred through December 31, 2015 and reflected in the fourteenth VCM report should be disallowed from rate base on the basis of imprudence; (ii) the Contractor Settlement Agreement was reasonable and prudent and none of the amounts paid pursuant to the Contractor Settlement Agreement should be disallowed from rate base on the basis of imprudence; (iii) (a) capital costs incurred up to $5.68 billion would be presumed to be reasonable and prudent with the burden of proof on any party challenging such costs, (b) Georgia Power would have the burden to show that any capital costs above $5.68 billion were prudent, and (c) a revised capital cost forecast of $7.3 billion (after reflecting the impact of payments received under the Guarantee Settlement Agreement and related Customer Refunds) was found reasonable; (iv) construction of Plant Vogtle Units 3 and 4 should be completed, with Southern Nuclear serving as project manager and Bechtel as primary contractor; (v) approved and deemed reasonable Georgia Power's revised schedule placing Plant Vogtle Units 3 and 4 in service in November 2021 and November 2022, respectively; (vi) confirmed that the revised cost forecast does not represent a cost cap and that prudence decisions on cost recovery will be made at a later date, consistent with applicable Georgia law; (vii) reduced the ROE used to calculate the NCCR tariff (a) from 10.95% (the ROE rate setting point authorized by the Georgia PSC in the 2013 ARP) to 10.00% effective January 1, 2016, (b) from 10.00% to 8.30% , effective January 1, 2020, and (c) from 8.30% to 5.30% , effective January 1, 2021 (provided that the ROE in no case will be less than Georgia Power's average cost of long-term debt); (viii) reduced the ROE used for AFUDC equity for Plant Vogtle Units 3 and 4 from 10.00% to Georgia Power's average cost of long-term debt, effective January 1, 2018; and (ix) agreed that upon Unit 3 reaching commercial operation, retail base rates would be adjusted to include carrying costs on those capital costs deemed prudent in the Vogtle Cost Settlement Agreement. The January 11, 2018 order also stated that if Plant Vogtle Units 3 and 4 are not commercially operational by June 1, 2021 and June 1, 2022, respectively, the ROE used to calculate the NCCR tariff will be further reduced by 10 basis points each month (but not lower than Georgia Power's average cost of long-term debt) until the respective Unit is commercially operational. The ROE reductions negatively impacted earnings by approximately $100 million in 2018 and are estimated to have negative earnings impacts of approximately $75 million in 2019 and an aggregate of approximately $635 million from 2020 to 2022. In its January 11, 2018 order, the Georgia PSC also stated if other conditions change and assumptions upon which Georgia Power's seventeenth VCM report are based do not materialize, the Georgia PSC reserved the right to reconsider the decision to continue construction. In February 2018, Georgia Interfaith Power & Light, Inc. (GIPL) and Partnership for Southern Equity, Inc. (PSE) filed a petition appealing the Georgia PSC's January 11, 2018 order with the Fulton County Superior Court. In March 2018, Georgia Watch filed a similar appeal to the Fulton County Superior Court for judicial review of the Georgia PSC's decision and denial of Georgia Watch's motion for reconsideration. In December 2018, the Fulton County Superior Court granted Georgia Power's motion to dismiss the two appeals. On January 9, 2019, GIPL, PSE, and Georgia Watch filed an appeal of this decision with the Georgia Court of Appeals. Georgia Power believes the appeal has no merit; however, an adverse outcome in the appeal combined with subsequent adverse action by the Georgia PSC could have a material impact on Southern Company's and Georgia Power's results of operations, financial condition, and liquidity. In August 2018, Georgia Power filed its nineteenth VCM report with the Georgia PSC, which requested approval of $578 million of construction capital costs incurred from January 1, 2018 through June 30, 2018. On February 19, 2019, the Georgia PSC approved the nineteenth VCM, but deferred approval of $51.6 million of expenditures related to Georgia Power's portion of an administrative claim filed in the Westinghouse bankruptcy proceedings. Through the nineteenth VCM, the Georgia PSC has approved total construction capital costs incurred through June 30, 2018 of $5.4 billion (before $1.7 billion of payments received under the Guarantee Settlement Agreement and approximately $188 million in related Customer Refunds). In addition, the staff of the Georgia PSC requested, and Georgia Power agreed, to report the results of the cost and schedule validation process to the Georgia PSC (which is expected to occur by May 1, 2019) and to file its twentieth VCM report concurrently with the twenty-first VCM report by August 31, 2019. The ultimate outcome of these matters cannot be determined at this time. DOE Financing At March 31, 2019 , Georgia Power had borrowed $3.46 billion related to Plant Vogtle Units 3 and 4 costs as provided through the Amended and Restated Loan Guarantee Agreement and related multi-advance credit facilities among Georgia Power, the DOE, and the FFB, which provide for borrowings of up to approximately $5.130 billion , subject to the satisfaction of certain conditions. See Note 8 to the financial statements under "Long-term Debt – DOE Loan Guarantee Borrowings" in Item 8 of the Form 10-K and Note (F) under " DOE Loan Guarantee Borrowings " for additional information, including applicable covenants, events of default, mandatory prepayment events, and conditions to borrowing. The ultimate outcome of these matters cannot be determined at this time. Mississippi Power Municipal and Rural Association Tariff On March 28, 2019, Mississippi Power filed a request with the FERC for a decrease in wholesale base revenues under the MRA tariff as agreed upon in a settlement agreement reached with its wholesale customers resolving all matters related to the Kemper County energy facility similar to the retail rate settlement agreement approved by the Mississippi PSC in February 2018 and reflecting the impacts of the Tax Reform Legislation. The MRA settlement agreement provides that base rates will decrease $3.7 million annually, effective January 1, 2019. Mississippi Power expects the matter to be resolved in the second quarter 2019. The ultimate outcome of this matter cannot be determined at this time. Kemper County Energy Facility As the mining permit holder, Liberty Fuels Company, LLC has a legal obligation to perform mine reclamation, and Mississippi Power has a contractual obligation to fund all reclamation activities. As a result of the abandonment of the Kemper IGCC, final mine reclamation began in 2018 and is expected to be substantially completed in 2020, with monitoring expected to continue through 2027. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. During the first quarter 2019, Mississippi Power recorded pre-tax charges to income of $2 million ( $1 million after tax), primarily resulting from the abandonment and related closure activities and ongoing period costs, net of sales proceeds, for the mine and gasifier-related assets at the Kemper County energy facility. Additional closure costs for the mine and gasifier-related assets, currently estimated at up to $10 million pre-tax (excluding salvage, net of dismantlement costs), may be incurred through the first half of 2020. In addition, period costs, including, but not limited to, costs for compliance and safety, ARO accretion, and property taxes for the mine and gasifier-related assets, are estimated at $11 million for the remainder of 2019 and $2 million to $6 million annually in 2020 through 2023. In addition, Mississippi Power constructed the CO 2 pipeline for the planned transport of captured CO 2 for use in enhanced oil recovery and is currently evaluating its options regarding the final disposition of the CO 2 pipeline, including removal of the pipeline. This evaluation is expected to be complete later in 2019. If Mississippi Power ultimately decides to remove the CO 2 pipeline, the cost of removal would have a material impact on Mississippi Power's financial statements and could have a material impact on Southern Company's financial statements. In December 2018, Mississippi Power filed with the DOE its request for property closeout certification under the contract related to the $387 million of grants received. Mississippi Power and the DOE are currently in discussions regarding the requested closeout and property disposition, which may require payment to the DOE for a portion of certain property that is to be retained by Mississippi Power. In connection with the DOE closeout discussions, on April 29, 2019, the Civil Division of the Department of Justice informed Southern Company and Mississippi Power of an investigation related to the Kemper County energy facility. The ultimate outcome of these matters cannot be determined at this time; however, they could have a material impact on Mississippi Power's and Southern Company's financial statements. Southern Company Gas Rate Proceedings Nicor Gas In November 2018, Nicor Gas filed a general base rate case with the Illinois Commission requesting a $230 million increase in annual base rate revenues. The requested increase is based on a projected test year for the 12 -month period ending September 30, 2020, a ROE of 10.6% , and an increase in the equity ratio from 52% to 54% to address the negative cash flow and credit metric impacts of the Tax Reform Legislation. On April 16, 2019, Nicor Gas entered into a stipulation agreement to resolve all related issues with the Staff of the Illinois Commission, including a ROE of 9.86% and an equity ratio of 54% . Also on April 16, 2019, Nicor Gas filed its rebuttal testimony with the Illinois Commission incorporating the stipulation agreement and addressing the remaining items outstanding with the other two intervenors. As a result of the stipulation agreement and rebuttal testimony, the revised requested annual revenue increase is $180 million . The Illinois Commission is expected to rule on the requested increase within the statutory time limit of 11 months from the filing of the rate case, after which rate adjustments will be effective. The ultimate outcome of this matter cannot be determined at this time. Virginia Natural Gas In December 2018, the Virginia Commission approved Virginia Natural Gas' annual information form filing, which reduced annual base rates by $14 million effective January 1, 2019 due to lower tax expense as a result of the Tax Reform Legislation. This approval also required Virginia Natural Gas to issue customer refunds, via bill credits, for $14 million related to 2018 tax benefits deferred as a regulatory liability, current, on the balance sheet at December 31, 2018. These customer refunds were completed in the first quarter 2019. Regulatory Infrastructure Programs Southern Company Gas is engaged in various infrastructure programs that update or expand its gas distribution systems to improve reliability and help ensure the safety of its utility infrastructure, and recovers in rates its investment and a return associated with these infrastructure programs. In addition to capital expenditures recovered through base rates by each of the natural gas distribution utilities, Nicor Gas and Virginia Natural Gas have separate rate riders that provide for timely recovery of capital expenditures for specific infrastructure replacement programs. Virginia Natural Gas On April 8, 2019, Virginia Natural Gas filed an application with the Virginia Commission to amend and extend its Steps to Advance Virginia's Energy program. The proposal would allow Virginia Natural Gas to continue replacing aging pipeline infrastructure and increase its authorized investment under the currently-approved plan. Virginia Natural Gas seeks to amend its currently-approved plan by increasing the authorized investment in 2019 from $35 million to $40 million and to extend the plan for an additional five years until 2024, with proposed annual investments of $50 million in 2020, $60 million in 2021, and $70 million in each year from 2022 through 2024, for a maximum total investment over the six - year term (2019 through 2024) of $370 million . The proposed investment schedule would also allow for variances of up to $6 million in 2019, $8 million in 2020, $9 million in 2021, and $10 million in each year from 2022 through 2024, with a total potential net variance of up to $10 million allowed for the program. The Virginia Commission is expected to rule on the request in the third quarter 2019. The ultimate outcome of this matter cannot be determined at this time. Affiliate Asset Management Agreements On March 15, 2019, the Virginia Commission approved an extension of Virginia Natural Gas' asset management agreement with Sequent to March 31, 2021. FERC Matters See Note 2 to the financial statements under "FERC Matters – Open Access Transmission Tariff" in Item 8 of the Form 10-K for additional information. On March 25, 2019, the Alabama Municipal Electric Authority and Cooperative Energy and SCS and the traditional electric operating companies filed a formal settlement agreement with the FERC agreeing to a rate reduction based on a 10.6% ROE, with a retroactive effective date of May 10, 2018, and a five -year moratorium on these parties seeking changes to the OATT formula rate. The ultimate outcome of this matter cannot be determined at this time; however, if approved by the FERC as filed, the OATT settlement would not have a material impact on the financial statements of any of the traditional electric operating companies or Southern Company.

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
CONTINGENCIES	CONTINGENCIES See Note 3 to the financial statements in Item 8 of the Form 10-K for information relating to various lawsuits and other contingencies. General Litigation Matters 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 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 by Monroe County Employees' Retirement System on behalf of all persons who purchased shares of Southern Company's common stock between April 25, 2012 and October 29, 2013. The complaint alleges that Southern Company, certain of its officers, and certain former Mississippi Power officers made materially false and misleading statements regarding the Kemper County energy facility in violation of certain provisions under the Securities Exchange Act of 1934, as amended. The complaint seeks, among other things, compensatory damages and litigation costs and attorneys' fees. In 2017, the plaintiffs filed an amended complaint that provided additional detail about their claims, increased the purported class period by one day, and added certain other former Mississippi Power officers as defendants. Also in 2017, the defendants filed a motion to dismiss the plaintiffs' amended complaint with prejudice, to which the plaintiffs filed an opposition. In March 2018, the court issued an order granting, in part, the defendants' motion to dismiss. The court dismissed certain claims against certain officers of Southern Company and Mississippi Power and dismissed the allegations related to a number of the statements that plaintiffs challenged as being false or misleading. In April 2018, the defendants filed a motion for reconsideration of the court's order, seeking dismissal of the remaining claims in the lawsuit. In August 2018, the court denied the motion for reconsideration and denied a motion to certify the issue for interlocutory appeal. In February 2017, Jean Vineyard and Judy Mesirov each filed a shareholder derivative lawsuit in the U.S. District Court for the Northern District of Georgia. Each of these lawsuits names as defendants Southern Company, certain of its directors, certain of its officers, and certain former Mississippi Power officers. In 2017, these two shareholder derivative lawsuits were consolidated in the U.S. District Court for the Northern District of Georgia. The complaints allege that the defendants caused Southern Company to make false or misleading statements regarding the Kemper County energy facility cost and schedule. Further, the complaints allege that the defendants were unjustly enriched and caused the waste of corporate assets and also allege that the individual defendants violated their fiduciary duties. Each plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and, on each plaintiff's own behalf, attorneys' fees and costs in bringing the lawsuit. Each plaintiff also seeks certain changes to Southern Company's corporate governance and internal processes. In April 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the 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, Georgia that names as defendants Southern Company, certain of its directors, certain of its officers, and certain former Mississippi Power officers. The complaint alleges that the individual defendants, among other things, breached their fiduciary duties in connection with schedule delays and cost overruns associated with the construction of the Kemper County energy facility. The complaint further alleges that the individual defendants authorized or failed to correct false and misleading statements regarding the Kemper County energy facility schedule and cost and failed to implement necessary internal controls to prevent harm to Southern Company. The plaintiff seeks to recover, on behalf of Southern Company, unspecified actual damages and disgorgement of profits and, on its behalf, attorneys' fees and costs in bringing the lawsuit. The plaintiff also seeks certain unspecified changes to Southern Company's corporate governance and internal processes. In May 2018, the court entered an order staying this lawsuit until 30 days after the resolution of any dispositive motions or any settlement, whichever is earlier, in the 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. The ultimate outcome of these matters cannot be determined at this time. Georgia Power In 2011, plaintiffs filed a putative class action against Georgia Power in the Superior Court of Fulton County, Georgia alleging that Georgia Power's collection in rates of amounts for municipal franchise fees (which fees are paid to municipalities) exceeded the amounts allowed in orders of the Georgia PSC and alleging certain state tort law claims. In 2016, the Georgia Court of Appeals reversed the trial court's previous dismissal of the case and remanded the case to the trial court. Georgia Power filed a petition for writ of certiorari with the Georgia Supreme Court, which was granted in 2017. In June 2018, the Georgia Supreme Court affirmed the judgment of the Georgia Court of Appeals and remanded the case to the trial court for further proceedings. Following a motion by Georgia Power, on February 13, 2019, the Superior Court of Fulton County ordered the parties to submit petitions to the Georgia PSC for a declaratory ruling to address certain terms the court previously held were ambiguous as used in the Georgia PSC's orders. The order entered by the Superior Court of Fulton County also conditionally certified the proposed class. In March 2019, Georgia Power and the plaintiffs filed petitions with the Georgia PSC seeking confirmation of the proper application of the municipal franchise fee schedule pursuant to the Georgia PSC's orders. Georgia Power and the plaintiffs also have filed notices of appeal with the Georgia Court of Appeals regarding the Superior Court of Fulton County's February 2019 order. Georgia Power believes the plaintiffs' claims have no merit. 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 May 2018, Southern Company and Mississippi Power received a notice of dispute and arbitration demand filed by Martin Product Sales, LLC (Martin) based on two agreements, both related to Kemper IGCC byproducts for which Mississippi Power provided termination notices in 2017. Martin alleges breach of contract, breach of good faith and fair dealing, fraud and misrepresentation, and civil conspiracy and makes a claim for damages in the amount of approximately $143 million , as well as additional unspecified damages, attorney's fees, costs, and interest. 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. The ultimate outcome of this matter cannot be determined at this time. In November 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 by applying an incorrect interest rate. The plaintiffs seek to recover, on behalf of themselves and their putative class, actual damages, punitive damages, pre-judgment interest, post-judgment interest, attorney's fees, and costs. In response to Mississippi Power and the Mississippi PSC each filing a motion to dismiss, the plaintiffs filed an amended complaint on March 14, 2019. The amended complaint included four additional plaintiffs and additional claims for gross negligence, reckless conduct, and intentional wrongdoing. Mississippi Power and the Mississippi PSC have each filed a motion to dismiss the amended complaint. 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. The ultimate outcome of this matter 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 2016, certain solar panels were damaged during installation by the construction contractor, McCarthy Building Companies, Inc. (McCarthy), and certain solar panels were damaged by a hail event that also occurred during construction. In connection therewith, Southern Power withheld payment of approximately $26 million to the construction contractor, which placed a lien on the Roserock facility for the same amount. In 2017, Roserock filed a lawsuit in the state district court in Pecos County, Texas against XL Insurance America, Inc. and North American Elite Insurance Company seeking recovery from an insurance policy for damages resulting from the hail event and McCarthy's installation practices. In June 2018, the court granted Roserock's motion for partial summary judgment, finding that the insurers were in breach of contract and in violation of the Texas Insurance Code for failing to pay any monies owed for the hail claim. Separate lawsuits were filed between Roserock and McCarthy, as well as other parties, and that litigation was consolidated in the U.S. District Court for the Western District of Texas. On April 18, 2019, Roserock and the parties to the state and federal lawsuits executed a settlement agreement and mutual release that resolves both lawsuits. Under the agreement, the lawsuits will be dismissed and McCarthy will release its lien following payments of all amounts (which are expected to occur in May 2019). Roserock will pay $26 million to McCarthy that was withheld and included in the original construction costs and will receive funds that will cover all related legal costs and the replacement costs of certain solar panels. In addition, during the first quarter 2019, Roserock received a partial payment of approximately $5 million in insurance proceeds toward the hail event. Any additional funds received in excess of the initial replacement costs are expected to be recognized as a gain when received by Roserock in the second quarter 2019, but are not expected to have a material impact on Southern Power's net income. Environmental Remediation The Southern Company system must comply with environmental laws and regulations governing the handling and disposal of waste and releases of hazardous substances. Under these various laws and regulations, the Southern Company system could incur substantial costs to clean up affected sites. The traditional electric operating companies and the natural gas distribution utilities in Illinois and Georgia have each received authority from their respective state PSCs or other applicable state regulatory agencies to recover approved environmental compliance costs through regulatory mechanisms. These regulatory mechanisms are adjusted annually or as necessary within limits approved by the state PSCs or other applicable state regulatory agencies. Georgia Power's environmental remediation liability was $18 million and $23 million as of March 31, 2019 and December 31, 2018 , respectively. Georgia Power has been designated or identified as a potentially responsible party at sites governed by the Georgia Hazardous Site Response Act and/or by the federal Comprehensive Environmental Response, Compensation, and Liability Act, and assessment and potential cleanup of such sites is expected. Southern Company Gas' environmental remediation liability was $289 million and $294 million as of March 31, 2019 and December 31, 2018 , respectively, based on the estimated cost of environmental investigation and remediation associated with known current and former manufactured gas plant operating sites. These environmental remediation expenditures are recoverable from customers through rate mechanisms approved by the applicable state regulatory agencies of the natural gas distribution utilities, with the exception of one site representing $2 million of the total accrued remediation costs. The ultimate outcome of these matters cannot be determined at this time; however, as a result of the regulatory treatment for environmental remediation expenses described above, the final disposition of these matters is not expected to have a material impact on the financial statements of Southern Company, Georgia Power, or Southern Company Gas. Other Matters Mississippi Power 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 by the FERC and the Mississippi PSC, and cannot be determined at this time. See Note (K) under " Southern Company " for information regarding the sale of Gulf Power.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
REVENUE FROM CONTRACTS WITH CUSTOMERS	REVENUE FROM CONTRACTS WITH CUSTOMERS The registrants generate revenues from a variety of sources, some of which are excluded from the scope of ASC 606, Revenue from Contracts with Customers (ASC 606), such as leases, derivatives, and certain cost recovery mechanisms. See Note 1 to the financial statements under "Recently Adopted Accounting Standards – Revenue" in Item 8 of the Form 10-K for additional information on the adoption of ASC 606 for revenue from contracts with customers and Note 1 to the financial statements under "Revenues" and "Other Taxes" in Item 8 of the Form 10-K for additional information on the revenue policies of the registrants. For additional information on revenues accounted for under other accounting guidance, see Notes (J) and (L) for energy-related derivative contracts and lessor revenues, respectively, Note 1 to the financial statements under "Revenues – Southern Company Gas" in Item 8 of the Form 10-K for alternative revenue programs at the natural gas distribution utilities, and Note 2 to the financial statements in Item 8 of the Form 10-K for cost recovery mechanisms. The following tables disaggregate revenue sources for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 For the Three Months Ended March 31, 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 1,288 $ 1,539 Commercial 1,093 1,243 Industrial 677 756 Other 26 30 Natural gas distribution revenues 1,163 1,224 Alternative revenue programs (b) (2 ) (24 ) Total retail electric and gas distribution revenues $ 4,245 $ 4,768 Wholesale energy revenues (c)(d) 367 472 Wholesale capacity revenues (d) 132 151 Other natural gas revenues (e)(f) 313 407 Other revenues (g) 355 574 Total operating revenues $ 5,412 $ 6,372 (a) Retail electric revenues include $8 million and $18 million of revenues accounted for as leases for the three months ended March 31, 2019 and 2018 , respectively, and a (net reduction) or net increase of $(103) million and $117 million for the three months ended March 31, 2019 and 2018 , respectively, from certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. (b) 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 $53 million and $93 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues accounted for as derivatives, primarily related to physical energy sales in the wholesale electricity market. (d) Wholesale energy and wholesale capacity revenues include $66 million and $25 million , respectively, for the three months ended March 31, 2019 and $69 million and $30 million , respectively, for the three months ended March 31, 2018 related to PPAs accounted for as leases. (e) Other natural gas revenues related to Southern Company Gas' energy and risk management activities are presented net of the related costs of those activities and include gross third-party revenues of $1.9 billion for each of the three months ended March 31, 2019 and 2018 , of which $1.2 billion and $1.1 billion , respectively, relates to contracts that are accounted for as derivatives. See Note (M) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (f) Other natural gas revenues for the three months ended March 31, 2019 include $9 million of revenues accounted for as leases. (g) Other revenues include $96 million and $90 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues not accounted for under ASC 606, including $31 million and $33 million in 2019 and 2018, respectively, accounted for as leases. Alabama Power Georgia Power Mississippi Power (in millions) For the Three Months Ended March 31, 2019 Operating revenues Retail revenues (a)(b) Residential $ 540 $ 688 $ 60 Commercial 354 674 65 Industrial 313 289 74 Other 6 17 4 Total retail electric revenues $ 1,213 $ 1,668 $ 203 Wholesale energy revenues (c) 94 18 78 Wholesale capacity revenues 27 14 1 Other revenues (b)(d) 74 133 5 Total operating revenues $ 1,408 $ 1,833 $ 287 For the Three Months Ended March 31, 2018 Operating revenues Retail revenues (a)(b) Residential $ 570 $ 744 $ 60 Commercial 371 717 62 Industrial 338 316 70 Other 6 21 2 Total retail electric revenues $ 1,285 $ 1,798 $ 194 Wholesale energy revenues (c) 101 40 98 Wholesale capacity revenues 24 14 4 Other revenues (b)(d) 63 109 6 Total operating revenues $ 1,473 $ 1,961 $ 302 (a) Retail revenues at Alabama Power, Georgia Power, and Mississippi Power include a net increase or (net reduction) of $(57) million , $(47) million , and $1 million , respectively, for the three months ended March 31, 2019 and $47 million , $10 million , and $76 million , respectively, for the three months ended March 31, 2018 related to certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. (b) Retail revenues and other revenues at Georgia Power include $8 million and $11 million , respectively, for the three months ended March 31, 2019 and $18 million and $33 million , respectively, for the three months ended March 31, 2018 of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power, Georgia Power, and Mississippi Power include $3 million , $4 million , and $1 million , respectively, for the three months ended March 31, 2019 and $5 million , $7 million , and $1 million , respectively, for the three months ended March 31, 2018 accounted for as derivatives primarily related to physical energy sales in the wholesale electricity market. (d) Other revenues at Alabama Power and Georgia Power include $28 million and $31 million , respectively, for the three months ended March 31, 2019 and $25 million and $26 million , respectively, for the three months ended March 31, 2018 of revenues not accounted for under ASC 606. For the Three Months Ended March 31, 2019 For the Three (in millions) Southern Power PPA capacity revenues (a) $ 127 $ 138 PPA energy revenues (a) 227 254 Non-PPA revenues (b) 85 115 Other revenues 4 2 Total operating revenues $ 443 $ 509 (a) PPA capacity revenues and PPA energy revenues include $41 million and $72 million , respectively, for the three months ended March 31, 2019 and $47 million and $76 million , respectively, for the three months ended March 31, 2018 related to PPAs accounted for as leases. (b) Non-PPA revenues include $45 million and $79 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues from short-term sales related to physical energy sales from uncovered capacity in the wholesale electricity market. For the Three Months Ended March 31, 2019 For the Three (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 601 $ 660 Commercial 170 192 Transportation 256 277 Industrial 17 17 Other 119 78 Alternative revenue programs (a) (2 ) (24 ) Total natural gas distribution revenues $ 1,161 $ 1,200 Gas pipeline investments (b) 8 8 Wholesale gas services (c) 66 146 Gas marketing services (d) 229 271 Other revenues 10 14 Total operating revenues $ 1,474 $ 1,639 (a) Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (b) Revenues from gas pipeline investments include $8 million for the three months ended March 31, 2019 accounted for as leases. (c) Wholesale gas services revenues are presented net of the related costs associated with its energy trading and risk management activities. Operating revenues, as presented, include gross third-party revenues of $1.9 billion for each of the three months ended March 31, 2019 and 2018 , of which $1.2 billion and $1.1 billion , respectively, relates to contracts accounted for as derivatives. See Note (M) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (d) Gas marketing services includes $6 million and $4 million for the three months ended March 31, 2019 and 2018 , respectively, 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 as of March 31, 2019 and December 31, 2018 : Receivables Contract Assets Contract Liabilities March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 (in millions) Southern Company (*) $ 2,522 $ 2,630 $ 84 $ 102 $ 62 $ 32 Alabama Power 514 520 1 — 10 12 Georgia Power 668 721 41 58 25 7 Mississippi Power 85 100 — — — — Southern Power 99 118 — — 4 11 Southern Company Gas 948 952 — — 1 2 (*) Includes amounts related to held for sale investments. As of March 31, 2019 and December 31, 2018 , Georgia Power had contract assets primarily related to unregulated service agreements where payment is contingent on project completion and fixed retail customer bill programs where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one-year contract term. Alabama Power had contract liabilities for outstanding performance obligations primarily related to extended service agreements. Contract liabilities for Georgia Power and Southern Power relate to cash collections recognized in advance of revenue for certain unregulated service agreements and certain levelized PPAs, respectively. Southern Company's unregulated distributed generation business had $34 million and $39 million of contract assets and $25 million and $11 million of contract liabilities at March 31, 2019 and December 31, 2018 , respectively, remaining for outstanding performance obligations. The following table reflects revenue from contracts with customers recognized in the three-month period ended March 31, 2019 included in the contract liability at December 31, 2018 : Three Months Ended March 31, 2019 (in millions) Southern Company $ 17 Southern Power 10 Revenues recognized in the three-month period ended March 31, 2019 , which were included in contract liabilities at December 31, 2018 , were immaterial for Alabama Power, Georgia Power, and Southern Company Gas. Remaining Performance Obligations The traditional electric operating companies and Southern Power have long-term contracts with customers in which revenues are recognized when the performance obligations are satisfied during 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. Registrants with revenues from contracts with customers related to these performance obligations remaining at March 31, 2019 expect the revenues to be recognized as follows: 2019 (remaining) 2020 2021 2022 2023 Thereafter (in millions) Southern Company (*) $ 451 $ 349 $ 315 $ 310 $ 301 $ 2,219 Alabama Power 16 22 27 23 22 140 Georgia Power 30 38 40 30 31 82 Mississippi Power 2 3 1 — — — Southern Power 248 295 270 276 269 2,143 (*) Includes amounts related to held for sale investments.

Consolidated Entities and Equit

Consolidated Entities and Equity Method Investments	3 Months Ended
	Mar. 31, 2019
Regulated Operations [Abstract]
CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS	CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS Southern Power Variable Interest Entities See Note 7 to the financial statements in Item 8 of the Form 10-K for additional information on Southern Power's VIEs. 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. Southern Power previously consolidated SP Solar and SP Wind. Southern Power continues to consolidate them following the 2018 sales of noncontrolling interests in each entity, as the primary beneficiary of each VIE, since it controls the most significant activities of each entity, including operating and maintaining their assets. Transfers and sales of the assets in the VIEs are subject to limited partner consent and the liabilities are non-recourse to the general credit of Southern Power. Liabilities consist of customary working capital items and do not include any long-term debt. SP Solar At March 31, 2019 , SP Solar had total assets of $6.5 billion , total liabilities of $373 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. SP Wind At March 31, 2019 , SP Wind had total assets of $2.6 billion , total liabilities of $141 million , and noncontrolling interests of $46 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. Southern Company Gas See Note 7 to the financial statements in Item 8 of the Form 10-K for additional information on Southern Company Gas' equity method investments. Equity Method Investments The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2019 and December 31, 2018 and related income from those investments for the three -month periods ended March 31, 2019 and 2018 were as follows: Investment Balance March 31, 2019 December 31, 2018 (in millions) SNG $ 1,262 $ 1,261 Atlantic Coast Pipeline 96 83 PennEast Pipeline 75 71 Other 124 123 Total $ 1,557 $ 1,538 Earnings from Equity Method Investments Three Months Ended Three Months (in millions) SNG $ 42 $ 39 Atlantic Coast Pipeline 3 1 PennEast Pipeline 2 1 Other 1 1 Total $ 48 $ 42 SNG Selected financial information of SNG for the three months ended March 31, 2019 and 2018 is as follows: Income Statement Information Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 (in millions) Revenues $ 166 $ 160 Operating income 106 99 Net income 84 78

Financing

Financing	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
FINANCING	FINANCING Bank Credit Arrangements Bank credit arrangements provide liquidity support to the registrants' commercial paper borrowings and the traditional electric operating companies' revenue bonds. The amount of variable rate revenue bonds of the traditional electric operating companies outstanding requiring liquidity support as of March 31, 2019 was approximately $1.4 billion (comprised of approximately $854 million at Alabama Power, $550 million at Georgia Power, and $40 million at Mississippi Power). In addition, at March 31, 2019 , the traditional electric operating companies had approximately $432 million (comprised of approximately $87 million at Alabama Power and $345 million at Georgia Power) of revenue bonds outstanding that were required to be remarketed within the next 12 months. Subsequent to March 31, 2019, Georgia Power purchased and held approximately $115 million of outstanding pollution control revenue bonds required to be remarketed. See Note 8 to the financial statements under "Bank Credit Arrangements" in Item 8 of the Form 10-K and " Financing Activities " herein for additional information. The following table outlines the committed credit arrangements by company as of March 31, 2019 : Expires Company 2019 2020 2022 Total Unused (d) (in millions) Southern Company (a) $ — $ — $ 2,000 $ 2,000 $ 1,999 Alabama Power 33 500 800 1,333 1,333 Georgia Power — — 1,750 1,750 1,736 Mississippi Power 100 — — 100 100 Southern Power (b) — — 750 750 741 Southern Company Gas (c) — — 1,900 1,900 1,895 Other 30 — — 30 30 Southern Company Consolidated $ 163 $ 500 $ 7,200 $ 7,863 $ 7,834 (a) Represents the Southern Company parent entity. (b) Does not include Southern Power Company's $120 million continuing letter of credit facility for standby letters of credit expiring in 2021, of which $24 million was unused at March 31, 2019 . Southern Power's subsidiaries are not parties to its bank credit arrangement. (c) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.4 billion of this arrangement. Southern Company Gas' committed credit arrangement also includes $500 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Pursuant to this multi-year credit arrangement, the allocations between Southern Company Gas Capital and Nicor Gas may be adjusted. (d) Amounts used are for letters of credit. 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. DOE Loan Guarantee Borrowings See Note 8 to the financial statements under "Long-term Debt – DOE Loan Guarantee Borrowings" in Item 8 of the Form 10-K for additional information regarding Georgia Power's 2014 loan guarantee agreement. Pursuant to the loan guarantee program established under Title XVII of the Energy Policy Act of 2005 (Title XVII Loan Guarantee Program), Georgia Power and the DOE entered into a loan guarantee agreement in 2014 and the Amended and Restated Loan Guarantee Agreement in March 2019. Under the Amended and Restated Loan Guarantee Agreement, the DOE has agreed to guarantee the obligations of Georgia Power under note purchase agreements among the DOE, Georgia Power, and the FFB and related promissory notes which provide for two multi-advance term loan facilities (FFB Credit Facilities). Under the FFB Credit Facilities, Georgia Power may make term loan borrowings through the FFB in an amount up to approximately $5.130 billion , provided that total aggregate borrowings under the FFB Credit Facilities may not exceed 70% of (i) Eligible Project Costs minus (ii) approximately $1.492 billion (reflecting the amounts received by Georgia Power under the Guarantee Settlement Agreement less the Customer Refunds). In March 2019, Georgia Power made borrowings under the FFB Credit Facilities in an aggregate principal amount of $835 million at an interest rate of 3.213% through the final maturity date of February 20, 2044. At March 31, 2019 , Georgia Power had a total of $3.46 billion of borrowings outstanding under the FFB Credit Facilities. All borrowings under the FFB Credit Facilities are full recourse to Georgia Power, and Georgia Power is obligated to reimburse the DOE for any payments the DOE is required to make to the FFB under its guarantee. Georgia Power's reimbursement obligations to the DOE are full recourse and secured by a first priority lien on (i) Georgia Power's 45.7% undivided ownership interest in Plant Vogtle Units 3 and 4 (primarily the units under construction, the related real property, and any nuclear fuel loaded in the reactor core) and (ii) Georgia Power's rights and obligations under the principal contracts relating to Plant Vogtle Units 3 and 4. There are no restrictions on Georgia Power's ability to grant liens on other property. In addition to the conditions described above, future advances are subject to satisfaction of customary conditions, as well as certification of compliance with the requirements of the Title XVII Loan Guarantee Program, including accuracy of project-related representations and warranties, delivery of updated project-related information, and evidence of compliance with the prevailing wage requirements of the Davis-Bacon Act of 1931, as amended, and certification from the DOE's consulting engineer that proceeds of the advances are used to reimburse Eligible Project Costs. Upon satisfaction of all conditions described above, advances may be requested on a quarterly basis through 2023. The final maturity date for each advance under the FFB Credit Facilities is February 20, 2044. Interest is payable quarterly and principal payments will begin on February 20, 2020. Borrowings under the FFB Credit Facilities will bear interest at the applicable U.S. Treasury rate plus a spread equal to 0.375% . Under the Amended and Restated Loan Guarantee Agreement, Georgia Power is subject to customary borrower affirmative and negative covenants and events of default. In addition, Georgia Power is subject to project-related reporting requirements and other project-specific covenants and events of default. In the event certain mandatory prepayment events occur, the FFB's commitment to make further advances under the FFB Credit Facilities will terminate and Georgia Power will be required to prepay the outstanding principal amount of all borrowings under the FFB Credit Facilities over a period of five years (with level principal amortization). Among other things, these mandatory prepayment events include (i) the termination of the Vogtle Services Agreement or rejection of the Vogtle Services Agreement in any Westinghouse bankruptcy if Georgia Power does not maintain access to intellectual property rights under the related intellectual property licenses; (ii) termination of the Bechtel Agreement, unless the Vogtle Owners enter into a replacement agreement; (iii) cancellation of Plant Vogtle Units 3 and 4 by the Georgia PSC or by Georgia Power; (iv) failure of the holders of 90% of the ownership interests in Plant Vogtle Units 3 and 4 to vote to continue construction following certain schedule extensions; (v) cost disallowances by the Georgia PSC that could have a material adverse effect on completion of Plant Vogtle Units 3 and 4 or Georgia Power's ability to repay the outstanding borrowings under the FFB Credit Facilities; or (vi) loss of or failure to receive necessary regulatory approvals. Under certain circumstances, insurance proceeds and any proceeds from an event of taking must be applied to immediately prepay outstanding borrowings under the FFB Credit Facilities. 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 Facilities 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 less the Customer Refunds. Georgia Power also may voluntarily prepay outstanding borrowings under the FFB Credit Facilities. Under the FFB Credit Facilities, any prepayment (whether mandatory or optional) will be made with a make-whole premium or discount, as applicable. In connection with any cancellation of Plant Vogtle Units 3 and 4, the DOE may elect to continue construction of Plant Vogtle Units 3 and 4. In such an event, the DOE will have the right to assume Georgia Power's rights and obligations under the principal agreements relating to Plant Vogtle Units 3 and 4 and to acquire all or a portion of Georgia Power's ownership interest in Plant Vogtle Units 3 and 4. Financing Activities The following table outlines the long-term debt financing activities for Southern Company and its subsidiaries for the first three months of 2019 : Company Senior Note Maturities, Redemptions, and Repurchases Revenue Bond Issuances and Reofferings of Purchased Bonds Revenue Bond and Other Long-Term Debt Issuances Other Long-Term Debt Redemptions and Maturities (a) (in millions) Southern Company (b) $ 2,100 $ — $ — $ — $ — Alabama Power 200 — — — — Georgia Power — 343 108 835 2 Mississippi Power — 43 — — — Other — — — — 19 Southern Company Consolidated $ 2,300 $ 386 $ 108 $ 835 $ 21 (a) Includes reductions in finance lease obligations resulting from cash payments under finance leases. (b) Represents the Southern Company parent entity. Except as otherwise described herein, Southern Company and its subsidiaries used the proceeds of debt issuances for their redemptions and maturities shown in the table above, to repay short-term indebtedness, and for general corporate purposes, including working capital. The subsidiaries also used the proceeds for their construction programs. Southern Company In January 2019, Southern Company repaid a $250 million short-term uncommitted bank credit arrangement and a $1.5 billion short-term floating rate bank loan. Also in January 2019, 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, following the completion of the cash tender offers, in February 2019, Southern Company completed the redemption of all of the Series 2018A Notes, 1.85% Notes, and Series 2014B Notes remaining outstanding. Georgia Power In January 2019, Georgia Power redeemed 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 March 2019, Georgia Power reoffered to the public the following pollution control revenue bonds that previously had been purchased and held by Georgia Power: • $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; • 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; and • $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. Subsequent to March 31, 2019, Georgia Power purchased and held the following pollution control revenue bonds, which may be reoffered to the public at a later date: • $55 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fourth Series 1994; • $30 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fourth Series 1995; • $20 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Ninth Series 1994; and • $10 million aggregate principal amount of Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 1994. Mississippi Power In March 2019, Mississippi Power reoffered to the public $43 million of Mississippi Business Finance Corporation Pollution Control Revenue Refunding Bonds, Series 2002, that previously had been purchased and held by Mississippi Power. Earnings per Share For Southern Company, the only difference in computing basic and diluted earnings per share is attributable to awards outstanding under stock-based compensation plans. See Note 12 to the financial statements in Item 8 of the Form 10-K for information on stock-based compensation plans. The effect of stock-based compensation plans was determined using the treasury stock method. Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 (in millions) As reported shares 1,038 1,011 Effect of stock-based compensation 7 5 Diluted shares 1,045 1,016 There were no stock-based compensation awards that were not included in the diluted earnings per share calculation because they were anti-dilutive for the three months ended March 31, 2019 and an immaterial amount of such awards was not included for the three months ended March 31, 2018 .

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES See Note 10 to the financial statements in Item 8 of the Form 10-K for additional tax information. Effective Tax Rate Details of significant changes in the effective tax rate for the applicable registrants are provided herein. Southern Company Southern Company's effective tax rate is typically lower than the statutory rate due to employee stock plans' dividend deduction, non-taxable AFUDC equity and flowback of excess deferred income taxes at the regulated utilities, and federal income tax benefits from ITCs and PTCs, primarily at Southern Power. Southern Company's effective tax rate was 39.8% for the three months ended March 31, 2019 compared to 10.8% for the corresponding period in 2018 . The effective tax rate increase was primarily due to the tax impact from the sale of Gulf Power. See Note (K) for additional information. Alabama Power Alabama Power's effective tax rate was 21.9% for the three months ended March 31, 2019 compared to 26.3% for the corresponding period in 2018. The effective tax rate decrease was primarily due to the application in 2018 of the accounting order approved by the Alabama PSC in May 2018 related to the Tax Reform Legislation. See Note 2 to the financial statements under "Alabama Power – Tax Reform Accounting Order" in Item 8 of the Form 10-K for additional information. Mississippi Power Mississippi Power's effective tax rate was 15.5% for the three months ended March 31, 2019 compared to a benefit rate of (34.7)% for the corresponding period in 2018 . The effective tax rate increase was primarily due to lower estimated losses on the Kemper IGCC in 2019, partially offset by an increase in the flowback of excess deferred income taxes as a result of a settlement agreement reached with wholesale customers under the MRA tariff. See Note (B) under "Mississippi Power" for additional information. Southern Power Southern Power's effective tax benefit rate was (49.8)% for the three months ended March 31, 2019 compared to (647.0)% for the corresponding period in 2018 . The effective tax benefit rate decrease was primarily due to changes in state apportionment rates following the reorganization of Southern Power's legal entities that own and operate certain solar facilities and a reduction of tax benefits from wind PTCs primarily as a result of the sale of a noncontrolling tax equity interest in SP Wind. Southern Company Gas Southern Company Gas' effective tax rate was 22.3% for the three months ended March 31, 2019 compared to 27.2% for the corresponding period in 2018 . This decrease was primarily related to tax impacts of the goodwill impairment charge recorded in the first quarter 2018 and an increase in the flowback of excess deferred income taxes in 2019 primarily at Atlanta Gas Light as previously authorized by the Georgia PSC. See Note 2 to the financial statements under "Southern Company Gas – Rate Proceedings" in Item 8 of the Form 10-K for additional information.

Retirement Benefits

Retirement Benefits	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
RETIREMENT BENEFITS	RETIREMENT BENEFITS The Southern Company system has a qualified defined benefit, trusteed, pension plan covering substantially all employees, with the exception of employees at PowerSecure. The qualified pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended (ERISA). No mandatory contributions to the qualified pension plan are anticipated for the year ending December 31, 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. See Note 11 to the financial statements in Item 8 of the Form 10-K for additional information. Components of the net periodic benefit costs for the three months ended March 31, 2019 and 2018 are presented in the following tables. Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 73 $ 17 $ 19 $ 3 $ 2 $ 6 Interest cost 123 28 39 6 1 9 Expected return on plan assets (221 ) (51 ) (73 ) (10 ) (2 ) (15 ) Amortization: Prior service costs — — — — — (1 ) Regulatory asset — — — — — 3 Net (gain)/loss 30 9 11 1 — 1 Net periodic pension cost (income) $ 5 $ 3 $ (4 ) $ — $ 1 $ 3 Postretirement Benefits Service cost $ 5 $ 1 $ 1 $ — $ — $ 1 Interest cost 17 4 7 1 — 2 Expected return on plan assets (16 ) (6 ) (6 ) — — (2 ) Amortization: Prior service costs 1 1 — — — — Regulatory asset — — — — — 2 Net (gain)/loss (1 ) — — — — (1 ) Net periodic postretirement benefit cost $ 6 $ — $ 2 $ 1 $ — $ 2 Three Months Ended March 31, 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 90 $ 19 $ 22 $ 4 $ 2 $ 8 Interest cost 116 25 35 5 1 10 Expected return on plan assets (236 ) (51 ) (74 ) (10 ) (3 ) (18 ) Amortization: Prior service costs 1 — — — — (1 ) Regulatory asset — — — — — 3 Net (gain)/loss 53 14 17 3 1 3 Net periodic pension cost (income) $ 24 $ 7 $ — $ 2 $ 1 $ 5 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ 1 Interest cost 19 4 7 1 — 2 Expected return on plan assets (17 ) (6 ) (6 ) — — (2 ) Amortization: Prior service costs 2 1 — — — — Regulatory asset — — — — — 1 Net (gain)/loss 3 — 2 — — — Net periodic postretirement benefit cost $ 13 $ — $ 5 $ 1 $ — $ 2

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS As of March 31, 2019 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using: As of March 31, 2019: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 322 $ 128 $ 4 $ — $ 454 Foreign currency derivatives — 38 — — 38 Investments in trusts: (c)(d) Domestic equity 682 120 — — 802 Foreign equity 60 195 — — 255 U.S. Treasury and government agency securities — 283 — — 283 Municipal bonds — 73 — — 73 Pooled funds – fixed income — 14 — — 14 Corporate bonds 24 298 — — 322 Mortgage and asset backed securities — 72 — — 72 Private equity — — — 48 48 Cash and cash equivalents 1 — — — 1 Other 28 4 — — 32 Cash equivalents 907 3 — — 910 Other investments 9 14 — — 23 Total $ 2,033 $ 1,242 $ 4 $ 48 $ 3,327 Liabilities: Energy-related derivatives (a)(b) $ 466 $ 106 $ 23 $ — $ 595 Interest rate derivatives — 35 — — 35 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 21 — 21 Total $ 466 $ 165 $ 44 $ — $ 675 Fair Value Measurements Using: As of March 31, 2019: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c) Domestic equity 446 108 — — 554 Foreign equity 60 57 — — 117 U.S. Treasury and government agency securities — 18 — — 18 Municipal bonds — 1 — — 1 Corporate bonds 24 139 — — 163 Mortgage and asset backed securities — 24 — — 24 Private equity — — — 48 48 Other 5 — — — 5 Cash equivalents 569 3 — — 572 Other investments — 14 — — 14 Total $ 1,104 $ 370 $ — $ 48 $ 1,522 Liabilities: Energy-related derivatives $ — $ 7 $ — $ — $ 7 Georgia Power Assets: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Nuclear decommissioning trusts: (c)(d) Domestic equity 236 1 — — 237 Foreign equity — 134 — — 134 U.S. Treasury and government agency securities — 265 — — 265 Municipal bonds — 72 — — 72 Corporate bonds — 160 — — 160 Mortgage and asset backed securities — 47 — — 47 Other 23 4 — — 27 Total $ 259 $ 692 $ — $ — $ 951 Liabilities: Energy-related derivatives $ — $ 16 $ — $ — $ 16 Interest rate derivatives — 2 — — 2 Total $ — $ 18 $ — $ — $ 18 Fair Value Measurements Using: As of March 31, 2019: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 202 — — — 202 Total $ 202 $ 3 $ — $ — $ 205 Liabilities: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Southern Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Foreign currency derivatives — 38 — — 38 Cash equivalents 10 — — — 10 Total $ 10 $ 39 $ — $ — $ 49 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 21 — 21 Total $ — $ 27 $ 21 $ — $ 48 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 322 $ 108 $ 4 $ — $ 434 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds – fixed income — 14 — — 14 Cash equivalents 1 — — — 1 Cash equivalents 13 — — — 13 Total $ 336 $ 137 $ 4 $ — $ 477 Liabilities: Energy-related derivatives (a)(b) $ 466 $ 73 $ 23 $ — $ 562 (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 $190 million . (c) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (d) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2019 , approximately $72 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. Southern Company, Alabama Power, and Georgia Power continue to elect the option to fair value investment securities held in the nuclear decommissioning trust funds. The fair value of the funds, including reinvested interest and dividends and excluding the funds' expenses, increased for the three months ended March 31, 2019 and decreased for the three months ended March 31, 2018 by the amounts shown in the table below. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively. Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 (in millions) Southern Company $ 152 $ (11 ) Alabama Power 87 (5 ) Georgia Power 65 (6 ) Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (J) for additional information on how these derivatives are used. For fair value measurements of the investments within the nuclear decommissioning trusts and the non-qualified deferred compensation trusts, external pricing vendors are designated for each asset class with each security specifically assigned a primary pricing source. For investments held within commingled funds, fair value is determined at the end of each business day through the net asset value, which is established by obtaining the underlying securities' individual prices from the primary pricing source. A market price secured from the primary source vendor is then evaluated by management in its valuation of the assets within the trusts. As a general approach, fixed income market pricing vendors gather market data (including indices and market research reports) and integrate relative credit information, observed market movements, and sector news into proprietary pricing models, pricing systems, and mathematical tools. Dealer quotes and other market information, including live trading levels and pricing analysts' judgments, are also obtained when available. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. See Note 6 to the financial statements under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. Southern Power has contingent payment obligations related to certain acquisitions whereby 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. As of March 31, 2019 , 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 $48 million and unfunded commitments related to the private equity investments totaled $49 million . 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. As of March 31, 2019 , other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (*) (in millions) Long-term debt, including securities due within one year: Carrying amount $ 42,535 $ 7,921 $ 10,910 $ 1,619 $ 4,995 $ 5,928 Fair value 43,910 8,424 11,249 1,619 5,131 6,176 (*) 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 Southern Company, Alabama Power, Georgia Power, Mississippi Power, Southern Power, and Southern Company Gas. Commodity Contracts with Level 3 Valuation Inputs As of March 31, 2019 , the fair value of Southern Company Gas' Level 3 physical natural gas forward contracts was $19 million . Since commodity contracts classified as Level 3 typically include a combination of observable and unobservable components, the changes in fair value may include amounts due in part to observable market factors, or changes to assumptions on the unobservable components. The following table includes transfers to Level 3, which represent the fair value of Southern Company Gas' commodity derivative contracts that include a significant unobservable component for the first time during the period. Three Months Ended March 31, 2019 (in millions) Beginning balance $ — Transfers to Level 3 (30 ) Changes in fair value 11 Ending balance $ (19 ) Changes in fair value of Level 3 instruments represent changes in gains and losses for the periods that are reported on Southern Company Gas' statements of income in natural gas revenues. The valuation of certain commodity contracts requires the use of certain unobservable inputs. All forward pricing used in the valuation of such contracts is directly based on third-party market data, such as broker quotes and exchange settlements, when that data is available. If third-party market data is not available, then industry standard methodologies are used to develop inputs that maximize the use of relevant observable inputs and minimize the use of unobservable inputs. Observable inputs, including some forward prices used for determining fair value, reflect the best available market information. Unobservable inputs are updated using industry standard techniques such as extrapolation, combining observable forward inputs supplemented by historical market and other relevant data. Level 3 physical natural gas forward contracts include unobservable forward price inputs (ranging from $0.07 to $1.15 per mmBtu). Forward price increases (decreases) as of March 31, 2019 would have resulted in higher (lower) values on a net basis.

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVES	DERIVATIVES Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Southern Company Gas' wholesale gas operations use various contracts in its commercial activities that generally meet the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (I) for additional fair value information. In the statements of cash flows, any cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Any cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with classification of the hedged interest or principal, respectively. See Note 1 to the financial statements under "Financial Instruments" in Item 8 of the Form 10-K for additional information. Energy-Related Derivatives The traditional electric operating companies, Southern Power, and Southern Company Gas enter into energy-related derivatives to hedge exposures to electricity, natural gas, and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, the traditional electric operating companies and the natural gas distribution utilities have limited exposure to market volatility in energy-related commodity prices. Each of the traditional electric operating companies and certain of the natural gas distribution utilities of Southern Company Gas manage fuel-hedging programs, implemented per the guidelines of their respective state PSCs or other applicable state regulatory agencies, through the use of financial derivative contracts, which are expected to continue to mitigate price volatility. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in operating revenues. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through 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 accumulated OCI before being recognized in the statements of income in the same period and in the same income statement line item as the earnings effect of the hedged transactions. • Not Designated — Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the electric and natural gas industries. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. At March 31, 2019 , the net volume of energy-related derivative contracts for natural gas positions, together with the longest hedge date over which the respective entity is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Net Purchased mmBtu Longest Hedge Date Longest Non-Hedge Date (in millions) Southern Company (*) 538 2022 2029 Alabama Power 72 2022 — Georgia Power 153 2022 — Mississippi Power 61 2022 — Southern Power 9 2020 — Southern Company Gas (*) 243 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 3.8 billion mmBtu and short natural gas positions of 3.6 billion mmBtu as of March 31, 2019 , which is also included in Southern Company's total volume. In addition to the volumes discussed above, the traditional electric operating companies and Southern Power enter into physical natural gas supply contracts that provide the option to sell back excess natural gas due to operational constraints. The maximum expected volume of natural gas subject to such a feature is 40 million mmBtu for Southern Company, which includes 6 million mmBtu for Alabama Power, 12 million mmBtu for Georgia Power, 5 million mmBtu for Mississippi Power, and 13 million mmBtu for Southern Power. For cash flow hedges of energy-related derivatives, the estimated pre-tax gains (losses) expected to be reclassified from accumulated OCI to earnings for the next 12 -month period ending March 31, 2020 are immaterial for all registrants. Interest Rate Derivatives Southern Company and certain subsidiaries may enter into interest rate derivatives to hedge exposure to changes in interest rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. At March 31, 2019 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value Gain (Loss) at March 31, 2019 (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month LIBOR+0.92% June 2020 $ (3 ) Southern Company (*) 1,500 2.35% 1-month LIBOR+0.87% July 2021 (30 ) Georgia Power 200 4.25% 3-month LIBOR+2.46% December 2019 (2 ) Southern Company Consolidated $ 2,000 $ (35 ) (*) Represents the Southern Company parent entity. The estimated pre-tax gains (losses) related to interest rate derivatives expected to be reclassified from accumulated OCI to interest expense for the next 12 -month period ending March 31, 2020 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 March 31, 2019 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at March 31, 2019 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 2 Southern Power 564 3.78% 500 1.85% June 2026 11 Total $ 1,241 € 1,100 $ 13 The estimated pre-tax gains (losses) related to Southern Power's foreign currency derivatives expected to be reclassified from accumulated OCI to earnings for the next 12 -month period ending March 31, 2020 are $(24) million . Derivative Financial Statement Presentation and Amounts Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas enter into derivative contracts that may contain certain provisions that permit intra-contract netting of derivative receivables and payables for routine billing and offsets related to events of default and settlements. Southern Company and certain subsidiaries also utilize master netting agreements to mitigate exposure to counterparty credit risk. These agreements may contain provisions that permit netting across product lines and against cash collateral. The fair value amounts of derivative assets and liabilities on the balance sheet are presented net to the extent that there are netting arrangements or similar agreements with the counterparties. The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 12 $ 10 $ 8 $ 23 Other deferred charges and assets/Other deferred credits and liabilities 11 21 9 26 Assets held for sale, current/Liabilities held for sale, current — — — 6 Total derivatives designated as hedging instruments for regulatory purposes $ 23 $ 31 $ 17 $ 55 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 3 $ 3 $ 7 Other deferred charges and assets/Other deferred credits and liabilities — 1 1 2 Interest rate derivatives: Other current assets/Other current liabilities — 20 — 19 Other deferred charges and assets/Other deferred credits and liabilities — 15 — 30 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 38 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 39 $ 63 $ 79 $ 81 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 259 $ 291 $ 561 $ 575 Other deferred charges and assets/Other deferred credits and liabilities 171 269 180 325 Total derivatives not designated as hedging instruments $ 430 $ 560 $ 741 $ 900 Gross amounts recognized $ 492 $ 654 $ 837 $ 1,036 Gross amounts offset (a) $ (333 ) $ (523 ) $ (524 ) $ (801 ) Net amounts recognized in the Balance Sheets (b) $ 159 $ 131 $ 313 $ 235 As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 2 $ 3 $ 4 Other deferred charges and assets/Other deferred credits and liabilities 3 5 3 6 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 7 $ 6 $ 10 Gross amounts recognized $ 6 $ 7 $ 6 $ 10 Gross amounts offset $ (5 ) $ (5 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 1 $ 2 $ 2 $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 4 $ 5 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities 5 11 4 13 Total derivatives designated as hedging instruments for regulatory purposes $ 9 $ 16 $ 6 $ 21 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 2 $ — $ 2 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 2 $ — $ 2 Gross amounts recognized $ 9 $ 18 $ 6 $ 23 Gross amounts offset $ (8 ) $ (8 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ 1 $ 10 $ — $ 17 As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 2 $ 1 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 1 4 2 6 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 6 $ 3 $ 9 Gross amounts recognized $ 3 $ 6 $ 3 $ 9 Gross amounts offset $ (3 ) $ (3 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ — $ 3 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 2 $ 3 $ 6 Other deferred charges and assets/Other deferred credits and liabilities — 1 1 2 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 38 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 39 $ 27 $ 79 $ 31 Gross amounts recognized $ 39 $ 27 $ 79 $ 31 Gross amounts offset $ (1 ) $ (1 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 38 $ 26 $ 76 $ 28 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 $ 3 $ 1 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities 1 — — 1 Total derivatives designated as hedging instruments for regulatory purposes $ 4 $ 1 $ 2 $ 9 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ — $ 1 $ — $ 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 1 $ — $ 1 As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 259 $ 291 $ 559 $ 574 Other deferred charges and assets/Other deferred credits and liabilities 171 269 180 325 Total derivatives not designated as hedging instruments $ 430 $ 560 $ 739 $ 899 Gross amounts of recognized $ 434 $ 562 $ 741 $ 909 Gross amounts offset (a) $ (316 ) $ (506 ) $ (508 ) $ (785 ) Net amounts recognized in the Balance Sheets (b) $ 118 $ 56 $ 233 $ 124 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $190 million and $277 million as of March 31, 2019 and December 31, 2018 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $11 million and $8 million as of March 31, 2019 and December 31, 2018 , respectively. At March 31, 2019 and December 31, 2018 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at March 31, 2019 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (5 ) $ (1 ) $ (2 ) $ (1 ) $ (1 ) Other regulatory assets, deferred (11 ) (2 ) (6 ) (3 ) — Other regulatory liabilities, current 7 1 1 1 4 Total energy-related derivative gains (losses) $ (9 ) $ (2 ) $ (7 ) $ (3 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $2 million at March 31, 2019 . Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2018 Derivative Category and Balance Sheet Location Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) Energy-related derivatives: Other regulatory assets, current $ (19 ) $ (3 ) $ (6 ) $ (2 ) $ (8 ) Other regulatory assets, deferred (16 ) (3 ) (9 ) (4 ) — Assets held for sale, current (6 ) — — — — Other regulatory liabilities, current 1 — — — 1 Total energy-related derivative gains (losses) $ (40 ) $ (6 ) $ (15 ) $ (6 ) $ (7 ) For the three months ended March 31, 2019 and 2018 , the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months 2019 2018 (in millions) Southern Company Energy-related derivatives $ — $ 12 Interest rate derivatives — (2 ) Foreign currency derivatives (39 ) 53 Total $ (39 ) $ 63 Southern Power Energy-related derivatives $ — $ 11 Foreign currency derivatives (39 ) 53 Total $ (39 ) $ 64 For the three months ended March 31, 2019 and 2018 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments on accumulated OCI were immaterial for the other registrants. For the three months ended March 31, 2019 and 2018 , the pre-tax effects of cash flow and fair value hedge accounting on income were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months 2019 2018 (in millions) Southern Company Total depreciation and amortization $ 751 $ 769 Gain (loss) on energy-related cash flow hedges (a) (3 ) 1 Total interest expense, net of amounts capitalized (430 ) (458 ) Gain (loss) on interest rate cash flow hedges (a) (5 ) (5 ) Gain (loss) on foreign currency cash flow hedges (a) (6 ) (5 ) Gain (loss) on interest rate fair value hedges (b) 14 (24 ) Total other income (expense), net 78 60 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) 36 Southern Power Total depreciation and amortization $ 119 $ 114 Gain (loss) on energy-related cash flow hedges (a) (3 ) 1 Total interest expense, net of amounts capitalized (44 ) (47 ) Gain (loss) on foreign currency cash flow hedges (a) (6 ) (5 ) Total other income (expense), net 2 3 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) 36 (a) Reclassified from accumulated OCI into earnings. (b) For fair value hedges, changes in the fair value of the derivative contracts are generally equal to changes in the fair value of the underlying debt and have no material impact on income. (c) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes. For the three months ended March 31, 2019 and 2018 , the pre-tax effects of cash flow and fair value hedge accounting on income for energy-related derivatives and interest rate derivatives were immaterial for the traditional electric operating companies and Southern Company Gas. As of March 31, 2019 and December 31, 2018, the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items As of March 31, 2019 As of December 31, 2018 As of March 31, 2019 As of December 31, 2018 (in millions) (in millions) Southern Company Securities due within one year $ (499 ) $ (498 ) $ 1 $ 2 Long-term debt (2,065 ) (2,052 ) 28 41 Georgia Power Securities due within one year $ (499 ) $ (498 ) $ 1 $ 2 Long-term debt — — — — For the three months ended March 31, 2019 and 2018 , the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income of Southern Company and Southern Company Gas were as follows: Gain (Loss) Three Months Ended March 31, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2019 2018 (in millions) Energy-related derivatives: Natural gas revenues (*) $ 33 $ (15 ) Cost of natural gas 8 2 Total derivatives in non-designated hedging relationships $ 41 $ (13 ) (*) Excludes immaterial gains (losses) recorded in natural gas revenues associated with weather derivatives for the three months ended March 31, 2019 and 2018 . For the three months ended March 31, 2019 and 2018 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments were immaterial f or the traditional electric operating companies and Southern Power. Contingent Features Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas do not have any credit arrangements that would require material changes in payment schedules or terminations as a result of a credit rating downgrade. There are certain derivatives that could require collateral, but not accelerated payment, in the event of various credit rating changes of certain Southern Company subsidiaries. At March 31, 2019 , the registrants had no collateral posted with derivative counterparties to satisfy these arrangements. For the registrants with interest rate derivatives at March 31, 2019 , the fair value of interest rate derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, was immaterial. At March 31, 2019 , the fair value of energy-related derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features, at a rating below BBB- and/or Baa3, were immaterial for all registrants. The maximum potential collateral requirements arising from the credit-risk-related contingent features for the traditional electric operating companies and Southern Power include certain agreements that could require collateral in the event that one or more Southern Company power pool participants has a credit rating change to below investment grade. Following the sale of Gulf Power to NextEra Energy, Gulf Power is continuing to participate in the Southern Company power pool for a defined transition period that, subject to certain potential adjustments, is scheduled to end on January 1, 2024. Generally, collateral may be provided by a Southern Company guaranty, letter of credit, or cash. If collateral is required, fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral are not offset against fair value amounts recognized for derivatives executed with the same counterparty. Alabama Power and Southern Power maintain accounts with certain regional transmission organizations to facilitate financial derivative transactions. Based on the value of the positions in these accounts and the associated margin requirements, Alabama Power and Southern Power may be required to post collateral. At March 31, 2019 , cash collateral posted in these accounts was immaterial. Southern Company Gas maintains accounts with brokers or the clearing houses of certain exchanges to facilitate financial derivative transactions. Based on the value of the positions in these accounts and the associated margin requirements, Southern Company Gas may be required to deposit cash into these accounts. At March 31, 2019 , cash collateral held on deposit in broker margin accounts was $190 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 Inc. 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	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
ACQUISITIONS AND DISPOSITIONS	ACQUISITIONS AND DISPOSITIONS See Note 15 to the financial statements in Item 8 of the Form 10-K for additional information. Southern Company On January 1, 2019, Southern Company completed the sale of all of the capital stock of Gulf Power to 700 Universe, LLC, a wholly-owned subsidiary of NextEra Energy, for an aggregate cash purchase price of approximately $5.8 billion (less $1.3 billion of indebtedness assumed), subject to customary working capital adjustments. The preliminary gain associated with the sale of Gulf Power totaled $2.5 billion pre-tax ( $1.3 billion after tax). The assets and liabilities of Gulf Power were classified as assets held for sale and liabilities held for sale on Southern Company's balance sheet as of December 31, 2018. Southern Power Construction Projects in Progress During the three months ended March 31, 2019 , Southern Power continued construction of the projects set forth in the table below. Total aggregate construction costs, excluding the acquisition costs, are expected to be between $575 million and $640 million for the Plant Mankato expansion and the Wildhorse Mountain and Reading facilities. At March 31, 2019 , total costs of construction incurred for these projects were $347 million and are included in CWIP, except for the Plant Mankato expansion, which is included in 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 Expected COD PPA Contract Period Mankato expansion (a) Natural Gas 385 Mankato, MN May 2019 20 years Wildhorse Mountain (b) Wind 100 Pushmataha County, OK Fourth quarter 2019 20 years Reading (c) Wind 200 Osage and Lyon Counties, KS Second quarter 2020 12 years (a) 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. This transaction is subject to FERC and state commission approvals and is expected to close mid-2019. The ultimate outcome of this matter cannot be determined at this time. See " Sales of Natural Gas and Biomass Plants " below. (b) In May 2018, Southern Power purchased 100% of the Wildhorse 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. (c) 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 Southern Power continues to evaluate and refine the deployment of the wind turbine equipment purchased in 2016 and 2017 to potential joint development and construction projects as well as the amount of MW capacity to be constructed. During the three months ended March 31, 2019, approximately $53 million of equipment was marketed for sale and, subsequent to March 31, 2019, was sold. At March 31, 2019, the equipment was classified as held for sale on Southern Company's and Southern Power's balance sheets. See " Assets Held for Sale " herein for additional information. The ultimate outcome of these matters cannot be determined at this time. Sales of Natural Gas and Biomass Plants In November 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. This transaction is subject to FERC and state commission approvals. 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 sheets as of March 31, 2019 and December 31, 2018. See " Assets Held for Sale " herein for additional information. On April 17, 2019, Southern Power entered into an agreement to sell all of its equity interests in the Nacogdoches biomass-fueled facility to Austin Energy for an aggregate purchase price of $460 million , subject to customary closing conditions and working capital adjustments. Each of these sales is expected to close in mid-2019; however, the ultimate outcome of these matters cannot be determined at this time. Assets Subject to Lien Under the terms of the PPA and the expansion PPA for Plant Mankato, approximately $538 million of assets, primarily related to property, plant, and equipment, are subject to lien at March 31, 2019 . Assets Held for Sale As discussed above, Southern Company and Southern Power each have assets and liabilities held for sale on their balance sheets at March 31, 2019 and 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 November 2018 for Plant Mankato, Southern Power ceased recognizing depreciation and amortization on the long-lived assets to be sold. The following table provides Southern Company's and Southern Power's major classes of assets and liabilities classified as held for sale at March 31, 2019 and December 31, 2018 : Southern Company Southern Power (in millions) At March 31, 2019 Assets Held for Sale: Current assets $ 55 $ 11 Total property, plant, and equipment 637 604 Goodwill and other intangible assets 82 40 Other non-current assets 44 — Total Assets Held for Sale $ 818 $ 655 Liabilities Held for Sale: Current liabilities $ 38 $ 9 Other non-current liabilities 39 — Total Liabilities Held for Sale $ 77 $ 9 At December 31, 2018 Assets Held for Sale: Current assets $ 393 $ 8 Total property, plant, and equipment 4,583 536 Goodwill and other intangible assets 40 40 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 and Southern Power each concluded that the sale of their assets, both individually and combined, did not represent a strategic shift in operations that has, or is expected to have, a major effect on its operations and financial results; therefore, none of the assets related to the sales have been classified as discontinued operations for any of the periods presented. Gulf Power and Southern Power's equity interests in Plant Oleander and Plant Stanton Unit A (together, the Florida Plants) represented individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax profit for these components for the three months ended March 31, 2018 is presented below: For the Three Months (in millions) Earnings before income taxes: Gulf Power $ 55 Southern Power's Florida Plants $ 8

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
LEASES	LEASES On January 1, 2019, the registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with right-of-use (ROU) assets that will be amortized over the term of each lease. The registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements are applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric generating units $ 1,094 $ 159 $ 1,606 $ — $ — $ — Real estate/land 803 3 63 2 393 83 Communication towers 131 1 3 — — — Railcars 55 25 26 3 — — Other 153 10 16 3 — 1 Total $ 2,236 $ 198 $ 1,714 $ 8 $ 393 $ 84 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 25 years while the land leases have remaining terms of up to 48 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies. Communication tower leases have terms of up to 10 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the affiliate PPA, which varies between four and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of approximately $670 million at March 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of March 31, 2019 . Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: As of March 31, 2019 Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Operating Leases Operating lease ROU assets, net $ 1,926 $ 160 $ 1,519 $ 8 $ 372 $ 86 Operating lease obligations - current $ 239 $ 47 $ 139 $ 3 $ 22 $ 13 Operating lease obligations - non current 1,752 147 1,404 5 371 71 Total operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance Leases Finance lease ROU assets, net $ 242 $ 4 $ 145 $ — $ — $ — Finance lease obligations - current $ 38 $ 1 $ 10 $ — $ — $ — Finance lease obligations - noncurrent 207 3 161 — — — Total finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — (*) Includes operating lease ROU assets, net and operating lease obligations classified as held for sale. Lease costs for the three months ended March 31, 2019 , which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease cost Operating lease cost $ 69 $ 7 $ 49 $ 1 $ 7 $ 4 Finance lease cost: Amortization of ROU assets 7 — 4 — — — Interest on lease obligations 3 — 4 — — — Total finance lease cost 10 — 8 — — — Short-term lease costs 14 5 3 — — — Variable lease cost 19 — 16 — 1 — Sublease income — — — — — — Total lease cost $ 112 $ 12 $ 76 $ 1 $ 8 $ 4 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 74 $ 13 $ 32 $ 1 $ 7 $ 4 Operating cash flows from finance leases 6 — 13 — — — Financing cash flows from finance leases 8 — 2 — — — ROU assets obtained in exchange for new operating lease obligations 15 2 4 — — — ROU assets obtained in exchange for new finance lease obligations 29 — 28 — — — As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Weighted-average remaining lease term in years: Operating leases 13.5 3.8 10.1 6.8 33.7 9.0 Finance leases 18.5 14.8 11.3 — — — Weighted-average discount rate: Operating leases 4.49 % 3.33 % 4.42 % 4.03 % 5.68 % 3.70 % Finance leases 5.00 % 3.75 % 10.68 % — % — % — % Maturities of lease liabilities are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2019 (remaining) $ 253 $ 46 $ 182 $ 2 $ 17 $ 12 2020 291 53 202 2 22 16 2021 274 52 197 1 23 16 2022 263 52 195 1 23 12 2023 198 3 196 1 24 10 Thereafter 1,637 1 984 2 848 36 Total 2,916 207 1,956 9 957 102 Less: Present value discount 925 13 413 1 564 18 Operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance leases: 2019 (remaining) $ 24 $ 1 $ 22 $ — $ — $ — 2020 32 1 28 — — — 2021 26 1 25 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — Thereafter 273 — 165 — — — Total 395 5 290 — — — Less: Present value discount 150 1 119 — — — Finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of March 31, 2019 , Southern Company and Southern Power have additional operating leases, primarily for land, that have not yet commenced. These operating leases are expected to commence during the remainder of 2019 through 2021, with lease terms of up to 30 years, and have estimated total obligations of $77 million . For additional information on each registrant's operating lease obligations at December 31, 2018, see Note 9 to the financial statements in Item 8 of the Form 10-K. Lessor With the exception of Southern Company Gas, the registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to five years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include tolling arrangements related to electric generating units accounted for as sales-type leases with terms of up to 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 28 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 24 years. Lease income for the three months ended March 31, 2019 is as follows: For the Three Months Ended March 31, 2019 Southern Company Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease income - interest income on sales-type leases $ 2 $ — $ 2 $ — $ — Lease income - operating leases 71 19 — 41 9 Variable lease income 66 — — 72 — Total lease income $ 139 $ 19 $ 2 $ 113 $ 9 No profit or loss was recognized by Mississippi Power upon commencement of a sales-type lease during the first quarter 2019. Lease income for Southern Power is included in wholesale revenues. Lease payments received under tolling arrangements and PPAs consist of either scheduled payments or variable payments based on the amount of energy produced by the underlying electric generating units. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. The undiscounted cash flows to be received under tolling arrangements accounted for as sales-type leases are as follows: As of March 31, 2019 Southern Company Mississippi Power (in millions) 2019 (remaining) $ 11 $ 11 2020 14 14 2021 14 14 2022 13 13 2023 12 12 Thereafter 135 135 Total undiscounted cash flows $ 199 $ 199 Lease receivable 108 108 Difference between undiscounted cash flows and discounted cash flows $ 91 $ 91 The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: As of March 31, 2019 Southern Company Georgia Power Southern Power Southern Company Gas (in millions) 2019 (remaining) $ 163 $ 20 $ 123 $ 26 2020 188 26 128 34 2021 183 18 131 34 2022 174 8 134 34 2023 171 2 137 34 Thereafter 1,809 — 1,017 498 Total $ 2,688 $ 74 $ 1,670 $ 660 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Southern Power allocates revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Alabama Power and Mississippi Power are immaterial.
LEASES	LEASES On January 1, 2019, the registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with right-of-use (ROU) assets that will be amortized over the term of each lease. The registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements are applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric generating units $ 1,094 $ 159 $ 1,606 $ — $ — $ — Real estate/land 803 3 63 2 393 83 Communication towers 131 1 3 — — — Railcars 55 25 26 3 — — Other 153 10 16 3 — 1 Total $ 2,236 $ 198 $ 1,714 $ 8 $ 393 $ 84 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 25 years while the land leases have remaining terms of up to 48 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies. Communication tower leases have terms of up to 10 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the affiliate PPA, which varies between four and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of approximately $670 million at March 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of March 31, 2019 . Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: As of March 31, 2019 Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Operating Leases Operating lease ROU assets, net $ 1,926 $ 160 $ 1,519 $ 8 $ 372 $ 86 Operating lease obligations - current $ 239 $ 47 $ 139 $ 3 $ 22 $ 13 Operating lease obligations - non current 1,752 147 1,404 5 371 71 Total operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance Leases Finance lease ROU assets, net $ 242 $ 4 $ 145 $ — $ — $ — Finance lease obligations - current $ 38 $ 1 $ 10 $ — $ — $ — Finance lease obligations - noncurrent 207 3 161 — — — Total finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — (*) Includes operating lease ROU assets, net and operating lease obligations classified as held for sale. Lease costs for the three months ended March 31, 2019 , which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease cost Operating lease cost $ 69 $ 7 $ 49 $ 1 $ 7 $ 4 Finance lease cost: Amortization of ROU assets 7 — 4 — — — Interest on lease obligations 3 — 4 — — — Total finance lease cost 10 — 8 — — — Short-term lease costs 14 5 3 — — — Variable lease cost 19 — 16 — 1 — Sublease income — — — — — — Total lease cost $ 112 $ 12 $ 76 $ 1 $ 8 $ 4 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 74 $ 13 $ 32 $ 1 $ 7 $ 4 Operating cash flows from finance leases 6 — 13 — — — Financing cash flows from finance leases 8 — 2 — — — ROU assets obtained in exchange for new operating lease obligations 15 2 4 — — — ROU assets obtained in exchange for new finance lease obligations 29 — 28 — — — As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Weighted-average remaining lease term in years: Operating leases 13.5 3.8 10.1 6.8 33.7 9.0 Finance leases 18.5 14.8 11.3 — — — Weighted-average discount rate: Operating leases 4.49 % 3.33 % 4.42 % 4.03 % 5.68 % 3.70 % Finance leases 5.00 % 3.75 % 10.68 % — % — % — % Maturities of lease liabilities are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2019 (remaining) $ 253 $ 46 $ 182 $ 2 $ 17 $ 12 2020 291 53 202 2 22 16 2021 274 52 197 1 23 16 2022 263 52 195 1 23 12 2023 198 3 196 1 24 10 Thereafter 1,637 1 984 2 848 36 Total 2,916 207 1,956 9 957 102 Less: Present value discount 925 13 413 1 564 18 Operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance leases: 2019 (remaining) $ 24 $ 1 $ 22 $ — $ — $ — 2020 32 1 28 — — — 2021 26 1 25 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — Thereafter 273 — 165 — — — Total 395 5 290 — — — Less: Present value discount 150 1 119 — — — Finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of March 31, 2019 , Southern Company and Southern Power have additional operating leases, primarily for land, that have not yet commenced. These operating leases are expected to commence during the remainder of 2019 through 2021, with lease terms of up to 30 years, and have estimated total obligations of $77 million . For additional information on each registrant's operating lease obligations at December 31, 2018, see Note 9 to the financial statements in Item 8 of the Form 10-K. Lessor With the exception of Southern Company Gas, the registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to five years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include tolling arrangements related to electric generating units accounted for as sales-type leases with terms of up to 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 28 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 24 years. Lease income for the three months ended March 31, 2019 is as follows: For the Three Months Ended March 31, 2019 Southern Company Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease income - interest income on sales-type leases $ 2 $ — $ 2 $ — $ — Lease income - operating leases 71 19 — 41 9 Variable lease income 66 — — 72 — Total lease income $ 139 $ 19 $ 2 $ 113 $ 9 No profit or loss was recognized by Mississippi Power upon commencement of a sales-type lease during the first quarter 2019. Lease income for Southern Power is included in wholesale revenues. Lease payments received under tolling arrangements and PPAs consist of either scheduled payments or variable payments based on the amount of energy produced by the underlying electric generating units. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. The undiscounted cash flows to be received under tolling arrangements accounted for as sales-type leases are as follows: As of March 31, 2019 Southern Company Mississippi Power (in millions) 2019 (remaining) $ 11 $ 11 2020 14 14 2021 14 14 2022 13 13 2023 12 12 Thereafter 135 135 Total undiscounted cash flows $ 199 $ 199 Lease receivable 108 108 Difference between undiscounted cash flows and discounted cash flows $ 91 $ 91 The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: As of March 31, 2019 Southern Company Georgia Power Southern Power Southern Company Gas (in millions) 2019 (remaining) $ 163 $ 20 $ 123 $ 26 2020 188 26 128 34 2021 183 18 131 34 2022 174 8 134 34 2023 171 2 137 34 Thereafter 1,809 — 1,017 498 Total $ 2,688 $ 74 $ 1,670 $ 660 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Southern Power allocates revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Alabama Power and Mississippi Power are immaterial.
LEASES	LEASES On January 1, 2019, the registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with right-of-use (ROU) assets that will be amortized over the term of each lease. The registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements are applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric generating units $ 1,094 $ 159 $ 1,606 $ — $ — $ — Real estate/land 803 3 63 2 393 83 Communication towers 131 1 3 — — — Railcars 55 25 26 3 — — Other 153 10 16 3 — 1 Total $ 2,236 $ 198 $ 1,714 $ 8 $ 393 $ 84 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 25 years while the land leases have remaining terms of up to 48 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies. Communication tower leases have terms of up to 10 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the affiliate PPA, which varies between four and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of approximately $670 million at March 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of March 31, 2019 . Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: As of March 31, 2019 Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Operating Leases Operating lease ROU assets, net $ 1,926 $ 160 $ 1,519 $ 8 $ 372 $ 86 Operating lease obligations - current $ 239 $ 47 $ 139 $ 3 $ 22 $ 13 Operating lease obligations - non current 1,752 147 1,404 5 371 71 Total operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance Leases Finance lease ROU assets, net $ 242 $ 4 $ 145 $ — $ — $ — Finance lease obligations - current $ 38 $ 1 $ 10 $ — $ — $ — Finance lease obligations - noncurrent 207 3 161 — — — Total finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — (*) Includes operating lease ROU assets, net and operating lease obligations classified as held for sale. Lease costs for the three months ended March 31, 2019 , which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease cost Operating lease cost $ 69 $ 7 $ 49 $ 1 $ 7 $ 4 Finance lease cost: Amortization of ROU assets 7 — 4 — — — Interest on lease obligations 3 — 4 — — — Total finance lease cost 10 — 8 — — — Short-term lease costs 14 5 3 — — — Variable lease cost 19 — 16 — 1 — Sublease income — — — — — — Total lease cost $ 112 $ 12 $ 76 $ 1 $ 8 $ 4 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 74 $ 13 $ 32 $ 1 $ 7 $ 4 Operating cash flows from finance leases 6 — 13 — — — Financing cash flows from finance leases 8 — 2 — — — ROU assets obtained in exchange for new operating lease obligations 15 2 4 — — — ROU assets obtained in exchange for new finance lease obligations 29 — 28 — — — As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Weighted-average remaining lease term in years: Operating leases 13.5 3.8 10.1 6.8 33.7 9.0 Finance leases 18.5 14.8 11.3 — — — Weighted-average discount rate: Operating leases 4.49 % 3.33 % 4.42 % 4.03 % 5.68 % 3.70 % Finance leases 5.00 % 3.75 % 10.68 % — % — % — % Maturities of lease liabilities are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2019 (remaining) $ 253 $ 46 $ 182 $ 2 $ 17 $ 12 2020 291 53 202 2 22 16 2021 274 52 197 1 23 16 2022 263 52 195 1 23 12 2023 198 3 196 1 24 10 Thereafter 1,637 1 984 2 848 36 Total 2,916 207 1,956 9 957 102 Less: Present value discount 925 13 413 1 564 18 Operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance leases: 2019 (remaining) $ 24 $ 1 $ 22 $ — $ — $ — 2020 32 1 28 — — — 2021 26 1 25 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — Thereafter 273 — 165 — — — Total 395 5 290 — — — Less: Present value discount 150 1 119 — — — Finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of March 31, 2019 , Southern Company and Southern Power have additional operating leases, primarily for land, that have not yet commenced. These operating leases are expected to commence during the remainder of 2019 through 2021, with lease terms of up to 30 years, and have estimated total obligations of $77 million . For additional information on each registrant's operating lease obligations at December 31, 2018, see Note 9 to the financial statements in Item 8 of the Form 10-K. Lessor With the exception of Southern Company Gas, the registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to five years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include tolling arrangements related to electric generating units accounted for as sales-type leases with terms of up to 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 28 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 24 years. Lease income for the three months ended March 31, 2019 is as follows: For the Three Months Ended March 31, 2019 Southern Company Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease income - interest income on sales-type leases $ 2 $ — $ 2 $ — $ — Lease income - operating leases 71 19 — 41 9 Variable lease income 66 — — 72 — Total lease income $ 139 $ 19 $ 2 $ 113 $ 9 No profit or loss was recognized by Mississippi Power upon commencement of a sales-type lease during the first quarter 2019. Lease income for Southern Power is included in wholesale revenues. Lease payments received under tolling arrangements and PPAs consist of either scheduled payments or variable payments based on the amount of energy produced by the underlying electric generating units. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. The undiscounted cash flows to be received under tolling arrangements accounted for as sales-type leases are as follows: As of March 31, 2019 Southern Company Mississippi Power (in millions) 2019 (remaining) $ 11 $ 11 2020 14 14 2021 14 14 2022 13 13 2023 12 12 Thereafter 135 135 Total undiscounted cash flows $ 199 $ 199 Lease receivable 108 108 Difference between undiscounted cash flows and discounted cash flows $ 91 $ 91 The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: As of March 31, 2019 Southern Company Georgia Power Southern Power Southern Company Gas (in millions) 2019 (remaining) $ 163 $ 20 $ 123 $ 26 2020 188 26 128 34 2021 183 18 131 34 2022 174 8 134 34 2023 171 2 137 34 Thereafter 1,809 — 1,017 498 Total $ 2,688 $ 74 $ 1,670 $ 660 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Southern Power allocates revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Alabama Power and Mississippi Power are immaterial.
LEASES	LEASES On January 1, 2019, the registrants adopted the provisions of FASB ASC Topic 842 (as amended), Leases (ASC 842), which require lessees to recognize leases with a term of greater than 12 months on the balance sheet as lease obligations, representing the discounted future fixed payments due, along with right-of-use (ROU) assets that will be amortized over the term of each lease. The registrants elected the transition methodology provided by ASC 842, whereby the applicable requirements are applied on a prospective basis as of the adoption date of January 1, 2019, without restating prior periods. The registrants also elected the package of practical expedients provided by ASC 842 that allows prior determinations of whether existing contracts are, or contain, leases and the classification of existing leases to continue without reassessment. Additionally, the registrants applied the use-of-hindsight practical expedient in determining lease terms as of the date of adoption and elected the practical expedient that allows existing land easements not previously accounted for as leases not to be reassessed. Lessee As lessee, the registrants lease certain electric generating units (including renewable energy facilities), real estate/land, communication towers, railcars, and other equipment and vehicles. The major categories of lease obligations are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric generating units $ 1,094 $ 159 $ 1,606 $ — $ — $ — Real estate/land 803 3 63 2 393 83 Communication towers 131 1 3 — — — Railcars 55 25 26 3 — — Other 153 10 16 3 — 1 Total $ 2,236 $ 198 $ 1,714 $ 8 $ 393 $ 84 Real estate/land leases primarily consist of commercial real estate leases at Southern Company, Georgia Power, and Southern Company Gas and various land leases primarily associated with renewable energy facilities at Southern Power. The commercial real estate leases have remaining terms of up to 25 years while the land leases have remaining terms of up to 48 years, including renewal periods. Communication towers are leased for the installation of equipment to provide cellular phone service to customers and to support the automated meter infrastructure programs at the traditional electric operating companies. Communication tower leases have terms of up to 10 years with options to renew for periods up to 20 years. While renewal options exist in many of the leases, other than for land leases associated with renewable energy facilities, the expected term used in calculating the lease obligation generally reflects only the noncancelable period of the lease as it is not considered reasonably certain that the lease will be extended. The expected term of land leases associated with renewable energy facilities includes renewal periods reasonably certain of exercise resulting in an expected lease term at least equal to the expected life of the renewable energy facilities. Contracts that Contain a Lease While not specifically structured as a lease, some of the PPAs at Alabama Power and Georgia Power are deemed to represent a lease of the underlying electric generating units when the terms of the PPA convey the right to control the use of the underlying assets. Amounts recorded for leases of electric generating units are generally based on the amount of scheduled capacity payments due over the remaining term of the affiliate PPA, which varies between four and 18 years. Georgia Power has several PPAs with Southern Power that Georgia Power accounts for as leases with a lease obligation of approximately $670 million at March 31, 2019 . The amount paid for energy under these affiliate PPAs reflects a price that would be paid in an arm's-length transaction as those amounts have been reviewed and approved by the Georgia PSC. Short-term Leases Leases with an initial term of 12 months or less are not recorded on the balance sheet; the registrants generally recognize lease expense for these leases on a straight-line basis over the lease term. Residual Value Guarantees Residual value guarantees exist primarily in railcar leases at Alabama Power and Georgia Power and the amounts probable of being paid under those guarantees are included in the lease payments. All such amounts are immaterial as of March 31, 2019 . Lease and Nonlease Components For all asset categories, with the exception of electric generating units, gas pipelines, and real estate leases, the registrants combine lease payments and any nonlease components, such as asset maintenance, for purposes of calculating the lease obligation and the right-of-use asset. Balance sheet amounts recorded for operating and finance leases are as follows: As of March 31, 2019 Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Operating Leases Operating lease ROU assets, net $ 1,926 $ 160 $ 1,519 $ 8 $ 372 $ 86 Operating lease obligations - current $ 239 $ 47 $ 139 $ 3 $ 22 $ 13 Operating lease obligations - non current 1,752 147 1,404 5 371 71 Total operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance Leases Finance lease ROU assets, net $ 242 $ 4 $ 145 $ — $ — $ — Finance lease obligations - current $ 38 $ 1 $ 10 $ — $ — $ — Finance lease obligations - noncurrent 207 3 161 — — — Total finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — (*) Includes operating lease ROU assets, net and operating lease obligations classified as held for sale. Lease costs for the three months ended March 31, 2019 , which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease cost Operating lease cost $ 69 $ 7 $ 49 $ 1 $ 7 $ 4 Finance lease cost: Amortization of ROU assets 7 — 4 — — — Interest on lease obligations 3 — 4 — — — Total finance lease cost 10 — 8 — — — Short-term lease costs 14 5 3 — — — Variable lease cost 19 — 16 — 1 — Sublease income — — — — — — Total lease cost $ 112 $ 12 $ 76 $ 1 $ 8 $ 4 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 74 $ 13 $ 32 $ 1 $ 7 $ 4 Operating cash flows from finance leases 6 — 13 — — — Financing cash flows from finance leases 8 — 2 — — — ROU assets obtained in exchange for new operating lease obligations 15 2 4 — — — ROU assets obtained in exchange for new finance lease obligations 29 — 28 — — — As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Weighted-average remaining lease term in years: Operating leases 13.5 3.8 10.1 6.8 33.7 9.0 Finance leases 18.5 14.8 11.3 — — — Weighted-average discount rate: Operating leases 4.49 % 3.33 % 4.42 % 4.03 % 5.68 % 3.70 % Finance leases 5.00 % 3.75 % 10.68 % — % — % — % Maturities of lease liabilities are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2019 (remaining) $ 253 $ 46 $ 182 $ 2 $ 17 $ 12 2020 291 53 202 2 22 16 2021 274 52 197 1 23 16 2022 263 52 195 1 23 12 2023 198 3 196 1 24 10 Thereafter 1,637 1 984 2 848 36 Total 2,916 207 1,956 9 957 102 Less: Present value discount 925 13 413 1 564 18 Operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance leases: 2019 (remaining) $ 24 $ 1 $ 22 $ — $ — $ — 2020 32 1 28 — — — 2021 26 1 25 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — Thereafter 273 — 165 — — — Total 395 5 290 — — — Less: Present value discount 150 1 119 — — — Finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — Payments made under PPAs at Georgia Power for energy generated from certain renewable energy facilities accounted for as operating and finance leases are considered variable lease costs and are therefore not reflected in the above maturity analysis. As of March 31, 2019 , Southern Company and Southern Power have additional operating leases, primarily for land, that have not yet commenced. These operating leases are expected to commence during the remainder of 2019 through 2021, with lease terms of up to 30 years, and have estimated total obligations of $77 million . For additional information on each registrant's operating lease obligations at December 31, 2018, see Note 9 to the financial statements in Item 8 of the Form 10-K. Lessor With the exception of Southern Company Gas, the registrants are each considered lessors in various arrangements that have been determined to contain a lease due to the customer's ability to control the use of the underlying asset owned by the applicable registrant. For the traditional electric operating companies, these arrangements consist of outdoor lighting contracts accounted for as operating leases with initial terms of up to five years, after which the contracts renew on a month-to-month basis at the customer's option. For Mississippi Power, these arrangements also include tolling arrangements related to electric generating units accounted for as sales-type leases with terms of up to 20 years. For Southern Power, these arrangements consist of PPAs related to electric generating units, including renewable energy facilities, accounted for as operating leases with terms of up to 28 years. For Southern Company, these arrangements also include PPAs related to fuel cells accounted for as operating leases with terms of up to 15 years. Southern Company Gas is the lessor in operating leases related to gas pipelines with remaining terms of up to 24 years. Lease income for the three months ended March 31, 2019 is as follows: For the Three Months Ended March 31, 2019 Southern Company Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease income - interest income on sales-type leases $ 2 $ — $ 2 $ — $ — Lease income - operating leases 71 19 — 41 9 Variable lease income 66 — — 72 — Total lease income $ 139 $ 19 $ 2 $ 113 $ 9 No profit or loss was recognized by Mississippi Power upon commencement of a sales-type lease during the first quarter 2019. Lease income for Southern Power is included in wholesale revenues. Lease payments received under tolling arrangements and PPAs consist of either scheduled payments or variable payments based on the amount of energy produced by the underlying electric generating units. Scheduled payments to be received under outdoor lighting contracts, tolling arrangements, and PPAs accounted for as leases are presented in the following maturity analyses. The undiscounted cash flows to be received under tolling arrangements accounted for as sales-type leases are as follows: As of March 31, 2019 Southern Company Mississippi Power (in millions) 2019 (remaining) $ 11 $ 11 2020 14 14 2021 14 14 2022 13 13 2023 12 12 Thereafter 135 135 Total undiscounted cash flows $ 199 $ 199 Lease receivable 108 108 Difference between undiscounted cash flows and discounted cash flows $ 91 $ 91 The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: As of March 31, 2019 Southern Company Georgia Power Southern Power Southern Company Gas (in millions) 2019 (remaining) $ 163 $ 20 $ 123 $ 26 2020 188 26 128 34 2021 183 18 131 34 2022 174 8 134 34 2023 171 2 137 34 Thereafter 1,809 — 1,017 498 Total $ 2,688 $ 74 $ 1,670 $ 660 Southern Power receives payments for renewable energy under PPAs accounted for as operating leases that are considered contingent rents and are therefore not reflected in the table above. Southern Power allocates revenue to the nonlease components of PPAs based on the stand-alone selling price of capacity and energy. The undiscounted cash flows to be received under outdoor lighting contracts accounted for as operating leases at Alabama Power and Mississippi Power are immaterial.

Segment and Related Information

Segment and Related Information	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
SEGMENT AND RELATED INFORMATION	SEGMENT AND RELATED INFORMATION Southern Company The primary businesses of the Southern Company system are electricity sales by the traditional electric operating companies and Southern Power and the distribution of natural gas by Southern Company Gas. The traditional electric operating companies – Alabama Power, Georgia Power, and Mississippi Power – are vertically integrated utilities providing electric service in three Southeastern states. Southern Power develops, constructs, acquires, owns, and manages power generation assets, including renewable energy projects, and sells electricity at market-based rates in the wholesale market. Southern Company Gas distributes natural gas through its natural gas distribution utilities and is involved in several other complementary businesses including gas pipeline investments, wholesale gas services, and gas marketing services. Southern Company's reportable business segments are the sale of electricity by the traditional electric operating companies, the sale of electricity in the competitive wholesale market by Southern Power, and the sale of natural gas and other complementary products and services by Southern Company Gas. Revenues from sales by Southern Power to the traditional electric operating companies were $87 million for the three months ended March 31, 2019 and $83 million for the three months ended March 31, 2018 . Revenues from sales of natural gas from Southern Company Gas to the traditional electric operating companies were immaterial for each of the three months ended March 31, 2019 and 2018 . Revenues from sales of natural gas from Southern Company Gas to Southern Power were $17 million for the three months ended March 31, 2019 and $36 million for the three months ended March 31, 2018 . The "All Other" column includes the Southern Company parent entity, which does not allocate operating expenses to business segments. Also, this category includes segments below the quantitative threshold for separate disclosure. These segments include providing energy technologies and services to electric utilities and large industrial, commercial, institutional, and municipal customers, as well as investments in telecommunications and leveraged lease projects. All other inter-segment revenues are not material. Financial data for business segments and products and services for the three months ended March 31, 2019 and 2018 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2019: Operating revenues $ 3,445 $ 443 $ (93 ) $ 3,795 $ 1,474 $ 182 $ (39 ) $ 5,412 Segment net income (loss) (a)(b)(c) 565 56 — 621 270 1,195 (2 ) 2,084 At March 31, 2019: Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 268 $ (1 ) $ 5,284 Total assets 76,798 15,104 (779 ) 91,123 20,952 3,391 (1,370 ) 114,096 Three Months Ended March 31, 2018: Operating revenues $ 3,979 $ 509 $ (106 ) $ 4,382 $ 1,639 $ 401 $ (50 ) $ 6,372 Segment net income (loss) (a)(b)(d) 612 121 — 733 279 (74 ) — 938 At December 31, 2018: Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 298 $ — $ 5,315 Total assets 79,382 14,883 (306 ) 93,959 21,448 3,285 (1,778 ) 116,914 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $2 million ( $1 million after tax) and $44 million ( $33 million after tax) for the three months ended March 31, 2019 and 2018 , respectively. See Note 2 to the financial statements in Item 8 of the Form 10-K and Note (B) under " Mississippi Power – Kemper County Energy Facility " for additional information. (c) Segment net income (loss) for the "All Other" column includes the preliminary pre-tax gain associated with the sale of Gulf Power of $2.5 billion ( $1.3 billion after tax) for the three months ended March 31, 2019. See Note (K) under " Southern Company " for additional information. (d) Segment net income (loss) for Southern Company Gas includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 related to the sale of Pivotal Home Solutions. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information. Products and Services Electric Utilities' Revenues Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2019 $ 3,084 $ 499 $ 212 $ 3,795 Three Months Ended March 31, 2018 3,568 623 191 4,382 Southern Company Gas' Revenues Gas (a) Gas (b) Other Total (in millions) Three Months Ended March 31, 2019 $ 1,161 $ 229 $ 84 $ 1,474 Three Months Ended March 31, 2018 1,200 271 168 1,639 (a) Operating revenues for the three gas distribution operations dispositions were $167 million for the three months ended March 31, 2018 . (b) Operating revenues for Pivotal Home Solutions were $32 million for the three months ended March 31, 2018 . 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. Gas distribution operations is the largest component of Southern Company Gas' business and includes natural gas local distribution utilities that construct, manage, and maintain intrastate natural gas pipelines and gas distribution facilities in four states. Gas pipeline investments consists of joint ventures in natural gas pipeline investments including a 50% interest in SNG, 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. 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 Energy Services, LLC. The all other column includes segments below the quantitative threshold for separate disclosure, including the storage and fuels operations, and the other subsidiaries that fall below the quantitative threshold for separate disclosure. Business segment financial data for the three months ended March 31, 2019 and 2018 was as follows: Gas Distribution Operations (a) Gas Pipeline Investments Wholesale Gas Services (b) Gas Marketing Services (c)(d) Total All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2019: Operating revenues $ 1,172 $ 8 $ 86 $ 229 $ 1,495 $ 11 $ (32 ) $ 1,474 Segment net income (loss) 133 32 47 61 273 (3 ) — 270 Total assets at March 31, 2019: 17,379 1,781 821 1,611 21,592 10,900 (11,540 ) 20,952 Three Months Ended March 31, 2018: Operating revenues $ 1,212 $ 8 $ 166 $ 271 $ 1,657 $ 15 $ (33 ) $ 1,639 Segment net income (loss) 149 27 104 13 293 (14 ) — 279 Total assets at December 31, 2018: 17,266 1,763 1,302 1,587 21,918 11,112 (11,582 ) $ 21,448 (a) Operating revenues for the three gas distribution operations dispositions were $167 million for the three months ended March 31, 2018. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information. (b) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) Three Months Ended March 31, 2019 $ 1,926 $ 88 $ 2,014 $ 1,928 $ 86 Three Months Ended March 31, 2018 1,938 167 2,105 1,939 166 (c) Operating revenues for the gas marketing services disposition were $32 million for the three months ended March 31, 2018. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information. (d) Segment net income (loss) for gas marketing services includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 related to the sale of Pivotal Home Solutions. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information.

Introduction (Policies)

Introduction (Policies)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting	The condensed quarterly financial statements of each registrant included herein have been prepared by such registrant, without audit, pursuant to the rules and regulations of the SEC. The Condensed Balance Sheets as of December 31, 2018 have been derived from the audited financial statements of each registrant. In the opinion of each registrant's management, the information regarding such registrant furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended March 31, 2019 and 2018 . Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although each registrant believes that the disclosures regarding such registrant are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for energy, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year.
Reclassifications	Certain prior year data presented in the financial statements have been reclassified to conform to the current year presentation. These reclassifications had no impact on the results of operations, financial position, or cash flows of any registrant.
Recently Adopted Accounting Standards	In 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changes the recognition, measurement, and presentation of expense associated with leases and provides clarification regarding the identification of certain components of contracts that would represent a lease. The accounting required by lessors is relatively unchanged and there is no change to the accounting for existing leveraged leases. The registrants adopted the new standard effective January 1, 2019. See Note (L) for additional information and related disclosures.
Goodwill and Other Intangible Assets	Goodwill is not amortized but is subject to an annual impairment test during the fourth quarter of each year or more frequently if impairment indicators arise.
Restricted Cash	At December 31, 2018, Georgia Power had restricted cash related to the redemption of pollution control revenue bonds, which were redeemed in January 2019. See Note (F) under " Financing Activities " for additional information. At both March 31, 2019 and December 31, 2018 , Southern Company Gas had restricted cash held as collateral for worker's compensation, life insurance, and long-term disability insurance.
Natural Gas For Sale	Southern Company Gas, with the exception of Nicor Gas, carries natural gas inventory on a WACOG basis. For any declines in market prices below the WACOG considered to be other than temporary, an adjustment is recorded to reduce the value of natural gas inventories to market value. Southern Company Gas had no material adjustment in any period presented. 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. Nicor Gas' inventory decrement at March 31, 2019 is expected to be restored prior to year end.
Valuation Methodologies	Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and over-the-counter financial products for natural gas and physical power products, including, from time to time, basis swaps. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices, power prices, implied volatility, and overnight index swap interest rates. Interest rate derivatives are also standard over-the-counter products that are valued using observable market data and assumptions commonly used by market participants. The fair value of interest rate derivatives reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and occasionally, implied volatility of interest rate options. The fair value of cross-currency swaps reflects the net present value of expected payments and receipts under the swap agreement based on the market's expectation of future foreign currency exchange rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk, and discount rates. The interest rate derivatives and cross-currency swaps are categorized as Level 2 under Fair Value Measurements as these inputs are based on observable data and valuations of similar instruments. See Note (J) for additional information on how these derivatives are used. For fair value measurements of the investments within the nuclear decommissioning trusts and the non-qualified deferred compensation trusts, external pricing vendors are designated for each asset class with each security specifically assigned a primary pricing source. For investments held within commingled funds, fair value is determined at the end of each business day through the net asset value, which is established by obtaining the underlying securities' individual prices from the primary pricing source. A market price secured from the primary source vendor is then evaluated by management in its valuation of the assets within the trusts. As a general approach, fixed income market pricing vendors gather market data (including indices and market research reports) and integrate relative credit information, observed market movements, and sector news into proprietary pricing models, pricing systems, and mathematical tools. Dealer quotes and other market information, including live trading levels and pricing analysts' judgments, are also obtained when available. The NRC requires licensees of commissioned nuclear power reactors to establish a plan for providing reasonable assurance of funds for future decommissioning. See Note 6 to the financial statements under "Nuclear Decommissioning" in Item 8 of the Form 10-K for additional information. 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.
Derivatives	Interest Rate Derivatives Southern Company and certain subsidiaries may enter into interest rate derivatives to hedge exposure to changes in interest rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and presented on the same income statement line item as the earnings effect of the hedged transactions. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings on the same income statement line item. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Foreign Currency Derivatives Southern Company and certain subsidiaries, including Southern Power, may enter into foreign currency derivatives to hedge exposure to changes in foreign currency exchange rates, such as that arising from the issuance of debt denominated in a currency other than U.S. dollars. Derivatives related to forecasted transactions are accounted for as cash flow hedges where the derivatives' fair value gains or losses are recorded in OCI and are reclassified into earnings at the same time and on the same income statement line as the earnings effect of the hedged transactions, including foreign currency gains or losses arising from changes in the U.S. currency exchange rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Southern Company, the traditional electric operating companies, Southern Power, and Southern Company Gas are exposed to market risks, including commodity price risk, interest rate risk, weather risk, and occasionally foreign currency exchange rate risk. To manage the volatility attributable to these exposures, each company nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to each company's policies in areas such as counterparty exposure and risk management practices. Southern Company Gas' wholesale gas operations use various contracts in its commercial activities that generally meet the definition of derivatives. For the traditional electric operating companies, Southern Power, and Southern Company Gas' other businesses, each company's policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (I) for additional fair value information. In the statements of cash flows, any cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Any cash impacts of settled foreign currency derivatives are classified as operating or financing activities to correspond with classification of the hedged interest or principal, respectively. See Note 1 to the financial statements under "Financial Instruments" in Item 8 of the Form 10-K for additional information. Energy-Related Derivatives The traditional electric operating companies, Southern Power, and Southern Company Gas enter into energy-related derivatives to hedge exposures to electricity, natural gas, and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, the traditional electric operating companies and the natural gas distribution utilities have limited exposure to market volatility in energy-related commodity prices. Each of the traditional electric operating companies and certain of the natural gas distribution utilities of Southern Company Gas manage fuel-hedging programs, implemented per the guidelines of their respective state PSCs or other applicable state regulatory agencies, through the use of financial derivative contracts, which are expected to continue to mitigate price volatility. The traditional electric operating companies (with respect to wholesale generating capacity) and Southern Power have limited exposure to market volatility in energy-related commodity prices because their long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, the traditional electric operating companies and Southern Power may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell electricity. Southern Company Gas retains exposure to price changes that can, in a volatile energy market, be material and can adversely affect its results of operations. Southern Company Gas also enters into weather derivative contracts as economic hedges of operating margins in the event of warmer-than-normal weather. Exchange-traded options are carried at fair value, with changes reflected in operating revenues. Non-exchange-traded options are accounted for using the intrinsic value method. Changes in the intrinsic value for non-exchange-traded contracts are reflected in operating revenues. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts designated as regulatory hedges relate primarily to the traditional electric operating companies' and the natural gas distribution utilities' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in fuel expense as the underlying fuel is used in operations and ultimately recovered through 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 accumulated OCI before being recognized in the statements of income in the same period and in the same income statement line item as the earnings effect of the hedged transactions. • Not Designated — Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the electric and natural gas industries. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. A

Introduction (Tables)

Introduction (Tables)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Goodwill	Goodwill at March 31, 2019 and December 31, 2018 was as follows: At March 31, 2019 At December 31, 2018 (in millions) Southern Company $ 5,284 $ 5,315 Southern Company Gas: Gas distribution operations $ 4,034 $ 4,034 Gas marketing services 981 981 Southern Company Gas total $ 5,015 $ 5,015
Schedule of Other Intangible Assets, Finite-Lived	Other intangible assets were as follows: At March 31, 2019 At December 31, 2018 Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 211 $ (100 ) $ 111 $ 223 $ (94 ) $ 129 Trade names 70 (22 ) 48 70 (21 ) 49 Storage and transportation contracts 64 (56 ) 8 64 (54 ) 10 PPA fair value adjustments 405 (67 ) 338 405 (61 ) 344 Other 11 (6 ) 5 11 (5 ) 6 Total other intangible assets subject to amortization $ 761 $ (251 ) $ 510 $ 773 $ (235 ) $ 538 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 836 $ (251 ) $ 585 $ 848 $ (235 ) $ 613 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 405 $ (67 ) $ 338 $ 405 $ (61 ) $ 344 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (89 ) $ 67 $ 156 $ (84 ) $ 72 Trade names 26 (8 ) 18 26 (7 ) 19 Wholesale gas services Storage and transportation contracts 64 (56 ) 8 64 (54 ) 10 Total other intangible assets subject to amortization $ 246 $ (153 ) $ 93 $ 246 $ (145 ) $ 101
Schedule of Other Intangible Assets, Indefinite-Lived	Other intangible assets were as follows: At March 31, 2019 At December 31, 2018 Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net Gross Carrying Amount Accumulated Amortization Other (in millions) (in millions) Southern Company Other intangible assets subject to amortization: Customer relationships $ 211 $ (100 ) $ 111 $ 223 $ (94 ) $ 129 Trade names 70 (22 ) 48 70 (21 ) 49 Storage and transportation contracts 64 (56 ) 8 64 (54 ) 10 PPA fair value adjustments 405 (67 ) 338 405 (61 ) 344 Other 11 (6 ) 5 11 (5 ) 6 Total other intangible assets subject to amortization $ 761 $ (251 ) $ 510 $ 773 $ (235 ) $ 538 Other intangible assets not subject to amortization: Federal Communications Commission licenses 75 — 75 75 — 75 Total other intangible assets $ 836 $ (251 ) $ 585 $ 848 $ (235 ) $ 613 Southern Power Other intangible assets subject to amortization: PPA fair value adjustments $ 405 $ (67 ) $ 338 $ 405 $ (61 ) $ 344 Southern Company Gas Other intangible assets subject to amortization: Gas marketing services Customer relationships $ 156 $ (89 ) $ 67 $ 156 $ (84 ) $ 72 Trade names 26 (8 ) 18 26 (7 ) 19 Wholesale gas services Storage and transportation contracts 64 (56 ) 8 64 (54 ) 10 Total other intangible assets subject to amortization $ 246 $ (153 ) $ 93 $ 246 $ (145 ) $ 101
Finite-lived Intangible Assets Amortization Expense	Amortization associated with other intangible assets was as follows: Three Months Ended March 31, 2019 (in millions) Southern Company $ 17 Southern Power (a) $ 6 Southern Company Gas Gas marketing services (b) $ 6 Wholesale gas services (a) 2 Southern Company Gas total $ 8 (a) Recorded as a reduction to operating revenues. (b) Included in depreciation and amortization.
Schedule of Cash and Cash Equivalents	The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amounts shown in the condensed statements of cash flows for the registrants that had restricted cash at March 31, 2019 and/or December 31, 2018 : Southern Company Southern Company Gas (in millions) At March 31, 2019 Cash and cash equivalents $ 1,361 $ 57 Restricted cash: Other accounts and notes receivable 4 4 Total cash, cash equivalents, and restricted cash $ 1,364 (*) $ 61 (*) Total does not add due to rounding. 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 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
Restrictions on Cash and Cash Equivalents	The following tables provide a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed balance sheets that total to the amounts shown in the condensed statements of cash flows for the registrants that had restricted cash at March 31, 2019 and/or December 31, 2018 : Southern Company Southern Company Gas (in millions) At March 31, 2019 Cash and cash equivalents $ 1,361 $ 57 Restricted cash: Other accounts and notes receivable 4 4 Total cash, cash equivalents, and restricted cash $ 1,364 (*) $ 61 (*) Total does not add due to rounding. 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 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

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Cost Recovery Clauses	The recovery balances for certain of Alabama Power's, Georgia Power's, and Mississippi Power's regulatory clauses at March 31, 2019 and December 31, 2018 were as follows: Regulatory Clause Balance Sheet Line Item March 31, December 31, (in millions) Alabama Power Rate CNP Compliance Deferred under recovered regulatory clause revenues $ — $ 42 Customer accounts receivable 25 — Rate CNP PPA Deferred under recovered regulatory clause revenues 21 25 Retail Energy Cost Recovery (*) Deferred under recovered regulatory clause revenues — 109 Other regulatory liabilities, deferred 2 — Natural Disaster Reserve Other regulatory liabilities, deferred 22 20 Georgia Power Fuel Cost Recovery Receivables – under recovered fuel clause revenues $ 73 $ 115 Mississippi Power Fuel Cost Recovery Over recovered retail fuel costs $ 10 $ 8 (*) In accordance with an accounting order issued on February 5, 2019 by the Alabama PSC, Alabama Power utilized $75 million of the 2018 Rate RSE refund liability to reduce the Rate ECR under recovered balance. See Note 2 to the financial statements under "Alabama Power – Rate ECR" in Item 8 of the Form 10-K for additional information.
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 March 31, 2019 (b) (4.9 ) Remaining estimate to complete (a) $ 3.5 (a) Excludes financing costs expected to be capitalized through AFUDC of approximately $325 million . (b) Net of $1.7 billion received from Toshiba under the Guarantee Settlement Agreement and approximately $188 million in related Customer Refunds.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following tables disaggregate revenue sources for the three months ended March 31, 2019 and 2018 : For the Three Months Ended March 31, 2019 For the Three Months Ended March 31, 2018 (in millions) Southern Company Operating revenues Retail electric revenues (a) Residential $ 1,288 $ 1,539 Commercial 1,093 1,243 Industrial 677 756 Other 26 30 Natural gas distribution revenues 1,163 1,224 Alternative revenue programs (b) (2 ) (24 ) Total retail electric and gas distribution revenues $ 4,245 $ 4,768 Wholesale energy revenues (c)(d) 367 472 Wholesale capacity revenues (d) 132 151 Other natural gas revenues (e)(f) 313 407 Other revenues (g) 355 574 Total operating revenues $ 5,412 $ 6,372 (a) Retail electric revenues include $8 million and $18 million of revenues accounted for as leases for the three months ended March 31, 2019 and 2018 , respectively, and a (net reduction) or net increase of $(103) million and $117 million for the three months ended March 31, 2019 and 2018 , respectively, from certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. (b) 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 $53 million and $93 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues accounted for as derivatives, primarily related to physical energy sales in the wholesale electricity market. (d) Wholesale energy and wholesale capacity revenues include $66 million and $25 million , respectively, for the three months ended March 31, 2019 and $69 million and $30 million , respectively, for the three months ended March 31, 2018 related to PPAs accounted for as leases. (e) Other natural gas revenues related to Southern Company Gas' energy and risk management activities are presented net of the related costs of those activities and include gross third-party revenues of $1.9 billion for each of the three months ended March 31, 2019 and 2018 , of which $1.2 billion and $1.1 billion , respectively, relates to contracts that are accounted for as derivatives. See Note (M) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (f) Other natural gas revenues for the three months ended March 31, 2019 include $9 million of revenues accounted for as leases. (g) Other revenues include $96 million and $90 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues not accounted for under ASC 606, including $31 million and $33 million in 2019 and 2018, respectively, accounted for as leases. Alabama Power Georgia Power Mississippi Power (in millions) For the Three Months Ended March 31, 2019 Operating revenues Retail revenues (a)(b) Residential $ 540 $ 688 $ 60 Commercial 354 674 65 Industrial 313 289 74 Other 6 17 4 Total retail electric revenues $ 1,213 $ 1,668 $ 203 Wholesale energy revenues (c) 94 18 78 Wholesale capacity revenues 27 14 1 Other revenues (b)(d) 74 133 5 Total operating revenues $ 1,408 $ 1,833 $ 287 For the Three Months Ended March 31, 2018 Operating revenues Retail revenues (a)(b) Residential $ 570 $ 744 $ 60 Commercial 371 717 62 Industrial 338 316 70 Other 6 21 2 Total retail electric revenues $ 1,285 $ 1,798 $ 194 Wholesale energy revenues (c) 101 40 98 Wholesale capacity revenues 24 14 4 Other revenues (b)(d) 63 109 6 Total operating revenues $ 1,473 $ 1,961 $ 302 (a) Retail revenues at Alabama Power, Georgia Power, and Mississippi Power include a net increase or (net reduction) of $(57) million , $(47) million , and $1 million , respectively, for the three months ended March 31, 2019 and $47 million , $10 million , and $76 million , respectively, for the three months ended March 31, 2018 related to certain cost recovery mechanisms that are not accounted for as revenue under ASC 606. (b) Retail revenues and other revenues at Georgia Power include $8 million and $11 million , respectively, for the three months ended March 31, 2019 and $18 million and $33 million , respectively, for the three months ended March 31, 2018 of revenues accounted for as leases. (c) Wholesale energy revenues at Alabama Power, Georgia Power, and Mississippi Power include $3 million , $4 million , and $1 million , respectively, for the three months ended March 31, 2019 and $5 million , $7 million , and $1 million , respectively, for the three months ended March 31, 2018 accounted for as derivatives primarily related to physical energy sales in the wholesale electricity market. (d) Other revenues at Alabama Power and Georgia Power include $28 million and $31 million , respectively, for the three months ended March 31, 2019 and $25 million and $26 million , respectively, for the three months ended March 31, 2018 of revenues not accounted for under ASC 606. For the Three Months Ended March 31, 2019 For the Three (in millions) Southern Power PPA capacity revenues (a) $ 127 $ 138 PPA energy revenues (a) 227 254 Non-PPA revenues (b) 85 115 Other revenues 4 2 Total operating revenues $ 443 $ 509 (a) PPA capacity revenues and PPA energy revenues include $41 million and $72 million , respectively, for the three months ended March 31, 2019 and $47 million and $76 million , respectively, for the three months ended March 31, 2018 related to PPAs accounted for as leases. (b) Non-PPA revenues include $45 million and $79 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues from short-term sales related to physical energy sales from uncovered capacity in the wholesale electricity market. For the Three Months Ended March 31, 2019 For the Three (in millions) Southern Company Gas Operating revenues Natural gas distribution revenues Residential $ 601 $ 660 Commercial 170 192 Transportation 256 277 Industrial 17 17 Other 119 78 Alternative revenue programs (a) (2 ) (24 ) Total natural gas distribution revenues $ 1,161 $ 1,200 Gas pipeline investments (b) 8 8 Wholesale gas services (c) 66 146 Gas marketing services (d) 229 271 Other revenues 10 14 Total operating revenues $ 1,474 $ 1,639 (a) Alternative revenue program revenues are presented net of any previously recognized program amounts billed to customers during the same accounting period. (b) Revenues from gas pipeline investments include $8 million for the three months ended March 31, 2019 accounted for as leases. (c) Wholesale gas services revenues are presented net of the related costs associated with its energy trading and risk management activities. Operating revenues, as presented, include gross third-party revenues of $1.9 billion for each of the three months ended March 31, 2019 and 2018 , of which $1.2 billion and $1.1 billion , respectively, relates to contracts accounted for as derivatives. See Note (M) under " Southern Company Gas " for additional information on the components of wholesale gas services operating revenues. (d) Gas marketing services includes $6 million and $4 million for the three months ended March 31, 2019 and 2018 , respectively, of revenues not accounted for under ASC 606.
Contract with Customer, Asset and Liability and Revenue Recognized	The following table reflects revenue from contracts with customers recognized in the three-month period ended March 31, 2019 included in the contract liability at December 31, 2018 : Three Months Ended March 31, 2019 (in millions) Southern Company $ 17 Southern Power 10 The following table reflects the closing balances of receivables, contract assets, and contract liabilities related to revenues from contracts with customers as of March 31, 2019 and December 31, 2018 : Receivables Contract Assets Contract Liabilities March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 March 31, 2019 December 31, 2018 (in millions) Southern Company (*) $ 2,522 $ 2,630 $ 84 $ 102 $ 62 $ 32 Alabama Power 514 520 1 — 10 12 Georgia Power 668 721 41 58 25 7 Mississippi Power 85 100 — — — — Southern Power 99 118 — — 4 11 Southern Company Gas 948 952 — — 1 2 (*) Includes amounts related to held for sale investments.
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction	Registrants with revenues from contracts with customers related to these performance obligations remaining at March 31, 2019 expect the revenues to be recognized as follows: 2019 (remaining) 2020 2021 2022 2023 Thereafter (in millions) Southern Company (*) $ 451 $ 349 $ 315 $ 310 $ 301 $ 2,219 Alabama Power 16 22 27 23 22 140 Georgia Power 30 38 40 30 31 82 Mississippi Power 2 3 1 — — — Southern Power 248 295 270 276 269 2,143 (*) Includes amounts related to held for sale investments.

Consolidated Entities and Equ_2

Consolidated Entities and Equity Method Investments (Tables)	3 Months Ended
	Mar. 31, 2019
Regulated Operations [Abstract]
Equity Method Investments	The carrying amounts of Southern Company Gas' equity method investments as of March 31, 2019 and December 31, 2018 and related income from those investments for the three -month periods ended March 31, 2019 and 2018 were as follows: Investment Balance March 31, 2019 December 31, 2018 (in millions) SNG $ 1,262 $ 1,261 Atlantic Coast Pipeline 96 83 PennEast Pipeline 75 71 Other 124 123 Total $ 1,557 $ 1,538 Selected financial information of SNG for the three months ended March 31, 2019 and 2018 is as follows: Income Statement Information Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 (in millions) Revenues $ 166 $ 160 Operating income 106 99 Net income 84 78
Schedule of Other Nonoperating Income, by Component	Earnings from Equity Method Investments Three Months Ended Three Months (in millions) SNG $ 42 $ 39 Atlantic Coast Pipeline 3 1 PennEast Pipeline 2 1 Other 1 1 Total $ 48 $ 42

Financing (Tables)

Financing (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Credit Arrangements by Company	The following table outlines the committed credit arrangements by company as of March 31, 2019 : Expires Company 2019 2020 2022 Total Unused (d) (in millions) Southern Company (a) $ — $ — $ 2,000 $ 2,000 $ 1,999 Alabama Power 33 500 800 1,333 1,333 Georgia Power — — 1,750 1,750 1,736 Mississippi Power 100 — — 100 100 Southern Power (b) — — 750 750 741 Southern Company Gas (c) — — 1,900 1,900 1,895 Other 30 — — 30 30 Southern Company Consolidated $ 163 $ 500 $ 7,200 $ 7,863 $ 7,834 (a) Represents the Southern Company parent entity. (b) Does not include Southern Power Company's $120 million continuing letter of credit facility for standby letters of credit expiring in 2021, of which $24 million was unused at March 31, 2019 . Southern Power's subsidiaries are not parties to its bank credit arrangement. (c) Southern Company Gas, as the parent entity, guarantees the obligations of Southern Company Gas Capital, which is the borrower of $1.4 billion of this arrangement. Southern Company Gas' committed credit arrangement also includes $500 million for which Nicor Gas is the borrower and which is restricted for working capital needs of Nicor Gas. Pursuant to this multi-year credit arrangement, the allocations between Southern Company Gas Capital and Nicor Gas may be adjusted. (d) Amounts used are for letters of credit.
Schedule of Long-term Debt Financing Activities	The following table outlines the long-term debt financing activities for Southern Company and its subsidiaries for the first three months of 2019 : Company Senior Note Maturities, Redemptions, and Repurchases Revenue Bond Issuances and Reofferings of Purchased Bonds Revenue Bond and Other Long-Term Debt Issuances Other Long-Term Debt Redemptions and Maturities (a) (in millions) Southern Company (b) $ 2,100 $ — $ — $ — $ — Alabama Power 200 — — — — Georgia Power — 343 108 835 2 Mississippi Power — 43 — — — Other — — — — 19 Southern Company Consolidated $ 2,300 $ 386 $ 108 $ 835 $ 21 (a) Includes reductions in finance lease obligations resulting from cash payments under finance leases. (b) Represents the Southern Company parent entity.
Shares Used to Compute Diluted Earnings Per Share	Shares used to compute diluted earnings per share were as follows: Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 (in millions) As reported shares 1,038 1,011 Effect of stock-based compensation 7 5 Diluted shares 1,045 1,016

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Pension Plans and Postretirement Plans	Components of the net periodic benefit costs for the three months ended March 31, 2019 and 2018 are presented in the following tables. Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 73 $ 17 $ 19 $ 3 $ 2 $ 6 Interest cost 123 28 39 6 1 9 Expected return on plan assets (221 ) (51 ) (73 ) (10 ) (2 ) (15 ) Amortization: Prior service costs — — — — — (1 ) Regulatory asset — — — — — 3 Net (gain)/loss 30 9 11 1 — 1 Net periodic pension cost (income) $ 5 $ 3 $ (4 ) $ — $ 1 $ 3 Postretirement Benefits Service cost $ 5 $ 1 $ 1 $ — $ — $ 1 Interest cost 17 4 7 1 — 2 Expected return on plan assets (16 ) (6 ) (6 ) — — (2 ) Amortization: Prior service costs 1 1 — — — — Regulatory asset — — — — — 2 Net (gain)/loss (1 ) — — — — (1 ) Net periodic postretirement benefit cost $ 6 $ — $ 2 $ 1 $ — $ 2 Three Months Ended March 31, 2018 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Pension Plans Service cost $ 90 $ 19 $ 22 $ 4 $ 2 $ 8 Interest cost 116 25 35 5 1 10 Expected return on plan assets (236 ) (51 ) (74 ) (10 ) (3 ) (18 ) Amortization: Prior service costs 1 — — — — (1 ) Regulatory asset — — — — — 3 Net (gain)/loss 53 14 17 3 1 3 Net periodic pension cost (income) $ 24 $ 7 $ — $ 2 $ 1 $ 5 Postretirement Benefits Service cost $ 6 $ 1 $ 2 $ — $ — $ 1 Interest cost 19 4 7 1 — 2 Expected return on plan assets (17 ) (6 ) (6 ) — — (2 ) Amortization: Prior service costs 2 1 — — — — Regulatory asset — — — — — 1 Net (gain)/loss 3 — 2 — — — Net periodic postretirement benefit cost $ 13 $ — $ 5 $ 1 $ — $ 2

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on a Recurring Basis	As of March 31, 2019 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using: As of March 31, 2019: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Southern Company Assets: Energy-related derivatives (a)(b) $ 322 $ 128 $ 4 $ — $ 454 Foreign currency derivatives — 38 — — 38 Investments in trusts: (c)(d) Domestic equity 682 120 — — 802 Foreign equity 60 195 — — 255 U.S. Treasury and government agency securities — 283 — — 283 Municipal bonds — 73 — — 73 Pooled funds – fixed income — 14 — — 14 Corporate bonds 24 298 — — 322 Mortgage and asset backed securities — 72 — — 72 Private equity — — — 48 48 Cash and cash equivalents 1 — — — 1 Other 28 4 — — 32 Cash equivalents 907 3 — — 910 Other investments 9 14 — — 23 Total $ 2,033 $ 1,242 $ 4 $ 48 $ 3,327 Liabilities: Energy-related derivatives (a)(b) $ 466 $ 106 $ 23 $ — $ 595 Interest rate derivatives — 35 — — 35 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 21 — 21 Total $ 466 $ 165 $ 44 $ — $ 675 Fair Value Measurements Using: As of March 31, 2019: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Alabama Power Assets: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Nuclear decommissioning trusts: (c) Domestic equity 446 108 — — 554 Foreign equity 60 57 — — 117 U.S. Treasury and government agency securities — 18 — — 18 Municipal bonds — 1 — — 1 Corporate bonds 24 139 — — 163 Mortgage and asset backed securities — 24 — — 24 Private equity — — — 48 48 Other 5 — — — 5 Cash equivalents 569 3 — — 572 Other investments — 14 — — 14 Total $ 1,104 $ 370 $ — $ 48 $ 1,522 Liabilities: Energy-related derivatives $ — $ 7 $ — $ — $ 7 Georgia Power Assets: Energy-related derivatives $ — $ 9 $ — $ — $ 9 Nuclear decommissioning trusts: (c)(d) Domestic equity 236 1 — — 237 Foreign equity — 134 — — 134 U.S. Treasury and government agency securities — 265 — — 265 Municipal bonds — 72 — — 72 Corporate bonds — 160 — — 160 Mortgage and asset backed securities — 47 — — 47 Other 23 4 — — 27 Total $ 259 $ 692 $ — $ — $ 951 Liabilities: Energy-related derivatives $ — $ 16 $ — $ — $ 16 Interest rate derivatives — 2 — — 2 Total $ — $ 18 $ — $ — $ 18 Fair Value Measurements Using: As of March 31, 2019: Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Net Asset Value as a Practical Expedient (NAV) Total (in millions) Mississippi Power Assets: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Cash equivalents 202 — — — 202 Total $ 202 $ 3 $ — $ — $ 205 Liabilities: Energy-related derivatives $ — $ 6 $ — $ — $ 6 Southern Power Assets: Energy-related derivatives $ — $ 1 $ — $ — $ 1 Foreign currency derivatives — 38 — — 38 Cash equivalents 10 — — — 10 Total $ 10 $ 39 $ — $ — $ 49 Liabilities: Energy-related derivatives $ — $ 3 $ — $ — $ 3 Foreign currency derivatives — 24 — — 24 Contingent consideration — — 21 — 21 Total $ — $ 27 $ 21 $ — $ 48 Southern Company Gas Assets: Energy-related derivatives (a)(b) $ 322 $ 108 $ 4 $ — $ 434 Non-qualified deferred compensation trusts: Domestic equity — 11 — — 11 Foreign equity — 4 — — 4 Pooled funds – fixed income — 14 — — 14 Cash equivalents 1 — — — 1 Cash equivalents 13 — — — 13 Total $ 336 $ 137 $ 4 $ — $ 477 Liabilities: Energy-related derivatives (a)(b) $ 466 $ 73 $ 23 $ — $ 562 (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 $190 million . (c) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (d) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. As of March 31, 2019 , approximately $72 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information.
Schedule of Increase (Decrease) In Fair Value Of Funds	The fair value of the funds, including reinvested interest and dividends and excluding the funds' expenses, increased for the three months ended March 31, 2019 and decreased for the three months ended March 31, 2018 by the amounts shown in the table below. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively. Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 (in millions) Southern Company $ 152 $ (11 ) Alabama Power 87 (5 ) Georgia Power 65 (6 )
Financial Instruments for Which Carrying Amount Did Not Equal Fair Value	As of March 31, 2019 , other financial instruments for which the carrying amount did not equal fair value were as follows: Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (*) (in millions) Long-term debt, including securities due within one year: Carrying amount $ 42,535 $ 7,921 $ 10,910 $ 1,619 $ 4,995 $ 5,928 Fair value 43,910 8,424 11,249 1,619 5,131 6,176 (*) 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.
Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component	The following table includes transfers to Level 3, which represent the fair value of Southern Company Gas' commodity derivative contracts that include a significant unobservable component for the first time during the period. Three Months Ended March 31, 2019 (in millions) Beginning balance $ — Transfers to Level 3 (30 ) Changes in fair value 11 Ending balance $ (19 )

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Energy-Related Derivatives	At March 31, 2019 , the net volume of energy-related derivative contracts for natural gas positions, together with the longest hedge date over which the respective entity is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Net Purchased mmBtu Longest Hedge Date Longest Non-Hedge Date (in millions) Southern Company (*) 538 2022 2029 Alabama Power 72 2022 — Georgia Power 153 2022 — Mississippi Power 61 2022 — Southern Power 9 2020 — Southern Company Gas (*) 243 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 3.8 billion mmBtu and short natural gas positions of 3.6 billion mmBtu as of March 31, 2019 , which is also included in Southern Company's total volume.
Schedule of Interest Rate Derivatives	At March 31, 2019 , the following interest rate derivatives were outstanding: Notional Amount Interest Rate Received Weighted Average Interest Rate Paid Hedge Maturity Date Fair Value Gain (Loss) at March 31, 2019 (in millions) (in millions) Fair Value Hedges of Existing Debt Southern Company (*) $ 300 2.75% 3-month LIBOR+0.92% June 2020 $ (3 ) Southern Company (*) 1,500 2.35% 1-month LIBOR+0.87% July 2021 (30 ) Georgia Power 200 4.25% 3-month LIBOR+2.46% December 2019 (2 ) Southern Company Consolidated $ 2,000 $ (35 ) (*) Represents the Southern Company parent entity.
Schedule of Foreign Currency Derivatives	At March 31, 2019 , the following foreign currency derivatives were outstanding: Pay Notional Pay Rate Receive Notional Receive Rate Hedge Fair Value Gain (Loss) at March 31, 2019 (in millions) (in millions) (in millions) Cash Flow Hedges of Existing Debt Southern Power $ 677 2.95% € 600 1.00% June 2022 $ 2 Southern Power 564 3.78% 500 1.85% June 2026 11 Total $ 1,241 € 1,100 $ 13
Fair Value of Energy-Related Derivatives and Interest Rate Derivatives	The fair value of energy-related derivatives, interest rate derivatives, and foreign currency derivatives was reflected in the balance sheets as follows: As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Southern Company Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 12 $ 10 $ 8 $ 23 Other deferred charges and assets/Other deferred credits and liabilities 11 21 9 26 Assets held for sale, current/Liabilities held for sale, current — — — 6 Total derivatives designated as hedging instruments for regulatory purposes $ 23 $ 31 $ 17 $ 55 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 3 $ 3 $ 7 Other deferred charges and assets/Other deferred credits and liabilities — 1 1 2 Interest rate derivatives: Other current assets/Other current liabilities — 20 — 19 Other deferred charges and assets/Other deferred credits and liabilities — 15 — 30 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 38 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 39 $ 63 $ 79 $ 81 Derivatives not designated as hedging instruments Energy-related derivatives: Other current assets/Other current liabilities $ 259 $ 291 $ 561 $ 575 Other deferred charges and assets/Other deferred credits and liabilities 171 269 180 325 Total derivatives not designated as hedging instruments $ 430 $ 560 $ 741 $ 900 Gross amounts recognized $ 492 $ 654 $ 837 $ 1,036 Gross amounts offset (a) $ (333 ) $ (523 ) $ (524 ) $ (801 ) Net amounts recognized in the Balance Sheets (b) $ 159 $ 131 $ 313 $ 235 As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Alabama Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 3 $ 2 $ 3 $ 4 Other deferred charges and assets/Other deferred credits and liabilities 3 5 3 6 Total derivatives designated as hedging instruments for regulatory purposes $ 6 $ 7 $ 6 $ 10 Gross amounts recognized $ 6 $ 7 $ 6 $ 10 Gross amounts offset $ (5 ) $ (5 ) $ (4 ) $ (4 ) Net amounts recognized in the Balance Sheets $ 1 $ 2 $ 2 $ 6 Georgia Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 4 $ 5 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities 5 11 4 13 Total derivatives designated as hedging instruments for regulatory purposes $ 9 $ 16 $ 6 $ 21 Derivatives designated as hedging instruments in cash flow and fair value hedges Interest rate derivatives: Other current assets/Other current liabilities $ — $ 2 $ — $ 2 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 2 $ — $ 2 Gross amounts recognized $ 9 $ 18 $ 6 $ 23 Gross amounts offset $ (8 ) $ (8 ) $ (6 ) $ (6 ) Net amounts recognized in the Balance Sheets $ 1 $ 10 $ — $ 17 As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Mississippi Power Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives: Other current assets/Other current liabilities $ 2 $ 2 $ 1 $ 3 Other deferred charges and assets/Other deferred credits and liabilities 1 4 2 6 Total derivatives designated as hedging instruments for regulatory purposes $ 3 $ 6 $ 3 $ 9 Gross amounts recognized $ 3 $ 6 $ 3 $ 9 Gross amounts offset $ (3 ) $ (3 ) $ (2 ) $ (2 ) Net amounts recognized in the Balance Sheets $ — $ 3 $ 1 $ 7 Southern Power Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Other current assets/Other current liabilities $ 1 $ 2 $ 3 $ 6 Other deferred charges and assets/Other deferred credits and liabilities — 1 1 2 Foreign currency derivatives: Other current assets/Other current liabilities — 24 — 23 Other deferred charges and assets/Other deferred credits and liabilities 38 — 75 — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 39 $ 27 $ 79 $ 31 Gross amounts recognized $ 39 $ 27 $ 79 $ 31 Gross amounts offset $ (1 ) $ (1 ) $ (3 ) $ (3 ) Net amounts recognized in the Balance Sheets $ 38 $ 26 $ 76 $ 28 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 $ 3 $ 1 $ 2 $ 8 Other deferred charges and assets/Other deferred credits and liabilities 1 — — 1 Total derivatives designated as hedging instruments for regulatory purposes $ 4 $ 1 $ 2 $ 9 Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ — $ 1 $ — $ 1 Total derivatives designated as hedging instruments in cash flow and fair value hedges $ — $ 1 $ — $ 1 As of March 31, 2019 As of December 31, 2018 Derivative Category and Balance Sheet Location Assets Liabilities Assets Liabilities (in millions) (in millions) Derivatives not designated as hedging instruments Energy-related derivatives: Assets from risk management activities/Liabilities from risk management activities-current $ 259 $ 291 $ 559 $ 574 Other deferred charges and assets/Other deferred credits and liabilities 171 269 180 325 Total derivatives not designated as hedging instruments $ 430 $ 560 $ 739 $ 899 Gross amounts of recognized $ 434 $ 562 $ 741 $ 909 Gross amounts offset (a) $ (316 ) $ (506 ) $ (508 ) $ (785 ) Net amounts recognized in the Balance Sheets (b) $ 118 $ 56 $ 233 $ 124 (a) Gross amounts offset include cash collateral held on deposit in broker margin accounts of $190 million and $277 million as of March 31, 2019 and December 31, 2018 , respectively. (b) Net amounts of derivative instruments outstanding exclude premium and intrinsic value associated with weather derivatives of $11 million and $8 million as of March 31, 2019 and December 31, 2018 , respectively.
Pre-tax Effects of Unrealized Derivative Gains (Losses) Arising from Energy-Related Derivative Instruments	At March 31, 2019 and December 31, 2018 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at March 31, 2019 Derivative Category and Balance Sheet Location Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Company Gas (*) (in millions) Energy-related derivatives: Other regulatory assets, current $ (5 ) $ (1 ) $ (2 ) $ (1 ) $ (1 ) Other regulatory assets, deferred (11 ) (2 ) (6 ) (3 ) — Other regulatory liabilities, current 7 1 1 1 4 Total energy-related derivative gains (losses) $ (9 ) $ (2 ) $ (7 ) $ (3 ) $ 3 (*) Fair value gains and losses recorded in regulatory assets and liabilities include cash collateral held on deposit in broker margin accounts of $2 million at March 31, 2019 . Regulatory Hedge Unrealized Gain (Loss) Recognized in the Balance Sheet at December 31, 2018 Derivative Category and Balance Sheet Location Southern Company Alabama Power Georgia Power Mississippi Power Southern Company Gas (in millions) Energy-related derivatives: Other regulatory assets, current $ (19 ) $ (3 ) $ (6 ) $ (2 ) $ (8 ) Other regulatory assets, deferred (16 ) (3 ) (9 ) (4 ) — Assets held for sale, current (6 ) — — — — Other regulatory liabilities, current 1 — — — 1 Total energy-related derivative gains (losses) $ (40 ) $ (6 ) $ (15 ) $ (6 ) $ (7 )
Pre-tax Effects of Interest Rate Derivatives, Designated as Cash Flow Hedging Instruments	For the three months ended March 31, 2019 and 2018 , the pre-tax effects of cash flow hedge accounting on accumulated OCI were as follows: Gain (Loss) Recognized in OCI on Derivative For the Three Months 2019 2018 (in millions) Southern Company Energy-related derivatives $ — $ 12 Interest rate derivatives — (2 ) Foreign currency derivatives (39 ) 53 Total $ (39 ) $ 63 Southern Power Energy-related derivatives $ — $ 11 Foreign currency derivatives (39 ) 53 Total $ (39 ) $ 64
Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location	For the three months ended March 31, 2019 and 2018 , the pre-tax effects of cash flow and fair value hedge accounting on income were as follows: Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships For the Three Months 2019 2018 (in millions) Southern Company Total depreciation and amortization $ 751 $ 769 Gain (loss) on energy-related cash flow hedges (a) (3 ) 1 Total interest expense, net of amounts capitalized (430 ) (458 ) Gain (loss) on interest rate cash flow hedges (a) (5 ) (5 ) Gain (loss) on foreign currency cash flow hedges (a) (6 ) (5 ) Gain (loss) on interest rate fair value hedges (b) 14 (24 ) Total other income (expense), net 78 60 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) 36 Southern Power Total depreciation and amortization $ 119 $ 114 Gain (loss) on energy-related cash flow hedges (a) (3 ) 1 Total interest expense, net of amounts capitalized (44 ) (47 ) Gain (loss) on foreign currency cash flow hedges (a) (6 ) (5 ) Total other income (expense), net 2 3 Gain (loss) on foreign currency cash flow hedges (a)(c) (24 ) 36 (a) Reclassified from accumulated OCI into earnings. (b) For fair value hedges, changes in the fair value of the derivative contracts are generally equal to changes in the fair value of the underlying debt and have no material impact on income. (c) The reclassification from accumulated OCI into other income (expense), net completely offsets currency gains and losses arising from changes in the U.S. currency exchange rates used to record the euro-denominated notes.
Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location	As of March 31, 2019 and December 31, 2018, the following amounts were recorded on the balance sheets related to cumulative basis adjustments for fair value hedges: Carrying Amount of the Hedged Item Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item Balance Sheet Location of Hedged Items As of March 31, 2019 As of December 31, 2018 As of March 31, 2019 As of December 31, 2018 (in millions) (in millions) Southern Company Securities due within one year $ (499 ) $ (498 ) $ 1 $ 2 Long-term debt (2,065 ) (2,052 ) 28 41 Georgia Power Securities due within one year $ (499 ) $ (498 ) $ 1 $ 2 Long-term debt — — — —
Pre-tax Effect of Interest Rate and Energy Related Derivatives	For the three months ended March 31, 2019 and 2018 , the pre-tax effects of energy-related derivatives not designated as hedging instruments on the statements of income of Southern Company and Southern Company Gas were as follows: Gain (Loss) Three Months Ended March 31, Derivatives in Non-Designated Hedging Relationships Statements of Income Location 2019 2018 (in millions) Energy-related derivatives: Natural gas revenues (*) $ 33 $ (15 ) Cost of natural gas 8 2 Total derivatives in non-designated hedging relationships $ 41 $ (13 ) (*) Excludes immaterial gains (losses) recorded in natural gas revenues associated with weather derivatives for the three months ended March 31, 2019 and 2018 .

Acquisitions and Dispositions (

Acquisitions and Dispositions (Tables)	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Schedule of Construction Projects	Project Facility Resource Approximate Nameplate Capacity ( MW ) Location Expected COD PPA Contract Period Mankato expansion (a) Natural Gas 385 Mankato, MN May 2019 20 years Wildhorse Mountain (b) Wind 100 Pushmataha County, OK Fourth quarter 2019 20 years Reading (c) Wind 200 Osage and Lyon Counties, KS Second quarter 2020 12 years (a) 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. This transaction is subject to FERC and state commission approvals and is expected to close mid-2019. The ultimate outcome of this matter cannot be determined at this time. See " Sales of Natural Gas and Biomass Plants " below. (b) In May 2018, Southern Power purchased 100% of the Wildhorse 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. (c) 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 Southern Power's equity interests in Plant Oleander and Plant Stanton Unit A (together, the Florida Plants) represented individually significant components of Southern Company and Southern Power, respectively; therefore, pre-tax profit for these components for the three months ended March 31, 2018 is presented below: For the Three Months (in millions) Earnings before income taxes: Gulf Power $ 55 Southern Power's Florida Plants $ 8 The following table provides Southern Company's and Southern Power's major classes of assets and liabilities classified as held for sale at March 31, 2019 and December 31, 2018 : Southern Company Southern Power (in millions) At March 31, 2019 Assets Held for Sale: Current assets $ 55 $ 11 Total property, plant, and equipment 637 604 Goodwill and other intangible assets 82 40 Other non-current assets 44 — Total Assets Held for Sale $ 818 $ 655 Liabilities Held for Sale: Current liabilities $ 38 $ 9 Other non-current liabilities 39 — Total Liabilities Held for Sale $ 77 $ 9 At December 31, 2018 Assets Held for Sale: Current assets $ 393 $ 8 Total property, plant, and equipment 4,583 536 Goodwill and other intangible assets 40 40 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

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Major Categories of Lease Obligations	The major categories of lease obligations are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Electric generating units $ 1,094 $ 159 $ 1,606 $ — $ — $ — Real estate/land 803 3 63 2 393 83 Communication towers 131 1 3 — — — Railcars 55 25 26 3 — — Other 153 10 16 3 — 1 Total $ 2,236 $ 198 $ 1,714 $ 8 $ 393 $ 84
Balance Sheet Amounts Recorded for Operating and Financing Leases	Balance sheet amounts recorded for operating and finance leases are as follows: As of March 31, 2019 Southern Company (*) Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Operating Leases Operating lease ROU assets, net $ 1,926 $ 160 $ 1,519 $ 8 $ 372 $ 86 Operating lease obligations - current $ 239 $ 47 $ 139 $ 3 $ 22 $ 13 Operating lease obligations - non current 1,752 147 1,404 5 371 71 Total operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance Leases Finance lease ROU assets, net $ 242 $ 4 $ 145 $ — $ — $ — Finance lease obligations - current $ 38 $ 1 $ 10 $ — $ — $ — Finance lease obligations - noncurrent 207 3 161 — — — Total finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ — (*) Includes operating lease ROU assets, net and operating lease obligations classified as held for sale.
Lease Costs and Other Information	Lease costs for the three months ended March 31, 2019 , which includes both amounts recognized as operations and maintenance expense and amounts capitalized as part of the cost of another asset, are as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease cost Operating lease cost $ 69 $ 7 $ 49 $ 1 $ 7 $ 4 Finance lease cost: Amortization of ROU assets 7 — 4 — — — Interest on lease obligations 3 — 4 — — — Total finance lease cost 10 — 8 — — — Short-term lease costs 14 5 3 — — — Variable lease cost 19 — 16 — 1 — Sublease income — — — — — — Total lease cost $ 112 $ 12 $ 76 $ 1 $ 8 $ 4 Georgia Power has variable lease payments that are based on the amount of energy produced by certain renewable generating facilities subject to PPAs. Other information with respect to cash and noncash activities related to leases, as well as weighted-average lease terms and discount rates, is as follows: For the Three Months Ended March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Other information Cash paid for amounts included in the measurements of lease obligations: Operating cash flows from operating leases $ 74 $ 13 $ 32 $ 1 $ 7 $ 4 Operating cash flows from finance leases 6 — 13 — — — Financing cash flows from finance leases 8 — 2 — — — ROU assets obtained in exchange for new operating lease obligations 15 2 4 — — — ROU assets obtained in exchange for new finance lease obligations 29 — 28 — — — As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas Weighted-average remaining lease term in years: Operating leases 13.5 3.8 10.1 6.8 33.7 9.0 Finance leases 18.5 14.8 11.3 — — — Weighted-average discount rate: Operating leases 4.49 % 3.33 % 4.42 % 4.03 % 5.68 % 3.70 % Finance leases 5.00 % 3.75 % 10.68 % — % — % — %
Maturities of Operating Lease Liabilities	Maturities of lease liabilities are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2019 (remaining) $ 253 $ 46 $ 182 $ 2 $ 17 $ 12 2020 291 53 202 2 22 16 2021 274 52 197 1 23 16 2022 263 52 195 1 23 12 2023 198 3 196 1 24 10 Thereafter 1,637 1 984 2 848 36 Total 2,916 207 1,956 9 957 102 Less: Present value discount 925 13 413 1 564 18 Operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance leases: 2019 (remaining) $ 24 $ 1 $ 22 $ — $ — $ — 2020 32 1 28 — — — 2021 26 1 25 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — Thereafter 273 — 165 — — — Total 395 5 290 — — — Less: Present value discount 150 1 119 — — — Finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ —
Maturities of Finance Lease Liabilities	Maturities of lease liabilities are as follows: As of March 31, 2019 Southern Company Alabama Power Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Maturity Analysis Operating leases: 2019 (remaining) $ 253 $ 46 $ 182 $ 2 $ 17 $ 12 2020 291 53 202 2 22 16 2021 274 52 197 1 23 16 2022 263 52 195 1 23 12 2023 198 3 196 1 24 10 Thereafter 1,637 1 984 2 848 36 Total 2,916 207 1,956 9 957 102 Less: Present value discount 925 13 413 1 564 18 Operating lease obligations $ 1,991 $ 194 $ 1,543 $ 8 $ 393 $ 84 Finance leases: 2019 (remaining) $ 24 $ 1 $ 22 $ — $ — $ — 2020 32 1 28 — — — 2021 26 1 25 — — — 2022 22 1 25 — — — 2023 18 1 25 — — — Thereafter 273 — 165 — — — Total 395 5 290 — — — Less: Present value discount 150 1 119 — — — Finance lease obligations $ 245 $ 4 $ 171 $ — $ — $ —
Lease Income, Sales-type Leases	Lease income for the three months ended March 31, 2019 is as follows: For the Three Months Ended March 31, 2019 Southern Company Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease income - interest income on sales-type leases $ 2 $ — $ 2 $ — $ — Lease income - operating leases 71 19 — 41 9 Variable lease income 66 — — 72 — Total lease income $ 139 $ 19 $ 2 $ 113 $ 9
Lease Income, Operating Leases	Lease income for the three months ended March 31, 2019 is as follows: For the Three Months Ended March 31, 2019 Southern Company Georgia Power Mississippi Power Southern Power Southern Company Gas (in millions) Lease income - interest income on sales-type leases $ 2 $ — $ 2 $ — $ — Lease income - operating leases 71 19 — 41 9 Variable lease income 66 — — 72 — Total lease income $ 139 $ 19 $ 2 $ 113 $ 9
Undiscounted Cash Flows to be Received Under Tolling Arrangements Accounted for as Sales-type Leases	The undiscounted cash flows to be received under tolling arrangements accounted for as sales-type leases are as follows: As of March 31, 2019 Southern Company Mississippi Power (in millions) 2019 (remaining) $ 11 $ 11 2020 14 14 2021 14 14 2022 13 13 2023 12 12 Thereafter 135 135 Total undiscounted cash flows $ 199 $ 199 Lease receivable 108 108 Difference between undiscounted cash flows and discounted cash flows $ 91 $ 91
Undiscounted Cash Flows to be Received Under PPAs Accounted for as Operating Leases	The undiscounted cash flows to be received under operating leases and contracts accounted for as operating leases (adjusted for intercompany eliminations) are as follows: As of March 31, 2019 Southern Company Georgia Power Southern Power Southern Company Gas (in millions) 2019 (remaining) $ 163 $ 20 $ 123 $ 26 2020 188 26 128 34 2021 183 18 131 34 2022 174 8 134 34 2023 171 2 137 34 Thereafter 1,809 — 1,017 498 Total $ 2,688 $ 74 $ 1,670 $ 660

Segment and Related Informati_2

Segment and Related Information (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Financial Data for Business Segments	Financial data for business segments and products and services for the three months ended March 31, 2019 and 2018 was as follows: Electric Utilities Traditional Electric Operating Companies Southern Power Eliminations Total Southern Company Gas All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2019: Operating revenues $ 3,445 $ 443 $ (93 ) $ 3,795 $ 1,474 $ 182 $ (39 ) $ 5,412 Segment net income (loss) (a)(b)(c) 565 56 — 621 270 1,195 (2 ) 2,084 At March 31, 2019: Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 268 $ (1 ) $ 5,284 Total assets 76,798 15,104 (779 ) 91,123 20,952 3,391 (1,370 ) 114,096 Three Months Ended March 31, 2018: Operating revenues $ 3,979 $ 509 $ (106 ) $ 4,382 $ 1,639 $ 401 $ (50 ) $ 6,372 Segment net income (loss) (a)(b)(d) 612 121 — 733 279 (74 ) — 938 At December 31, 2018: Goodwill $ — $ 2 $ — $ 2 $ 5,015 $ 298 $ — $ 5,315 Total assets 79,382 14,883 (306 ) 93,959 21,448 3,285 (1,778 ) 116,914 (a) Attributable to Southern Company. (b) Segment net income (loss) for the traditional electric operating companies includes pre-tax charges for estimated losses on plants under construction of $2 million ( $1 million after tax) and $44 million ( $33 million after tax) for the three months ended March 31, 2019 and 2018 , respectively. See Note 2 to the financial statements in Item 8 of the Form 10-K and Note (B) under " Mississippi Power – Kemper County Energy Facility " for additional information. (c) Segment net income (loss) for the "All Other" column includes the preliminary pre-tax gain associated with the sale of Gulf Power of $2.5 billion ( $1.3 billion after tax) for the three months ended March 31, 2019. See Note (K) under " Southern Company " for additional information. (d) Segment net income (loss) for Southern Company Gas includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 related to the sale of Pivotal Home Solutions. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information. Business segment financial data for the three months ended March 31, 2019 and 2018 was as follows: Gas Distribution Operations (a) Gas Pipeline Investments Wholesale Gas Services (b) Gas Marketing Services (c)(d) Total All Other Eliminations Consolidated (in millions) Three Months Ended March 31, 2019: Operating revenues $ 1,172 $ 8 $ 86 $ 229 $ 1,495 $ 11 $ (32 ) $ 1,474 Segment net income (loss) 133 32 47 61 273 (3 ) — 270 Total assets at March 31, 2019: 17,379 1,781 821 1,611 21,592 10,900 (11,540 ) 20,952 Three Months Ended March 31, 2018: Operating revenues $ 1,212 $ 8 $ 166 $ 271 $ 1,657 $ 15 $ (33 ) $ 1,639 Segment net income (loss) 149 27 104 13 293 (14 ) — 279 Total assets at December 31, 2018: 17,266 1,763 1,302 1,587 21,918 11,112 (11,582 ) $ 21,448 (a) Operating revenues for the three gas distribution operations dispositions were $167 million for the three months ended March 31, 2018. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information. (b) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Third Party Gross Revenues Intercompany Revenues Total Gross Revenues Less Gross Gas Costs Operating Revenues (in millions) Three Months Ended March 31, 2019 $ 1,926 $ 88 $ 2,014 $ 1,928 $ 86 Three Months Ended March 31, 2018 1,938 167 2,105 1,939 166 (c) Operating revenues for the gas marketing services disposition were $32 million for the three months ended March 31, 2018. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information. (d) Segment net income (loss) for gas marketing services includes a goodwill impairment charge of $42 million for the three months ended March 31, 2018 related to the sale of Pivotal Home Solutions. See Note 15 to the financial statements in Item 8 of the Form 10-K under "Southern Company Gas" for additional information.
Financial Data for Products and Services	Products and Services Electric Utilities' Revenues Retail Wholesale Other Total (in millions) Three Months Ended March 31, 2019 $ 3,084 $ 499 $ 212 $ 3,795 Three Months Ended March 31, 2018 3,568 623 191 4,382 Southern Company Gas' Revenues Gas (a) Gas (b) Other Total (in millions) Three Months Ended March 31, 2019 $ 1,161 $ 229 $ 84 $ 1,474 Three Months Ended March 31, 2018 1,200 271 168 1,639 (a) Operating revenues for the three gas distribution operations dispositions were $167 million for the three months ended March 31, 2018 . (b) Operating revenues for Pivotal Home Solutions were $32 million for the three months ended March 31, 2018 .

Introduction - Narrative (Detai

Introduction - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
SOUTHERN Co GAS
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventory decrement	$ 0	$ 0

Introduction - Goodwill (Detail

Introduction - Goodwill (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 5,284	$ 5,315
SOUTHERN Co GAS
Goodwill [Line Items]
Goodwill	5,015	$ 5,015
SOUTHERN Co GAS | Gas Distribution Operations
Goodwill [Line Items]
Goodwill	4,034
SOUTHERN Co GAS | Gas Marketing Services
Goodwill [Line Items]
Goodwill	$ 981

Introduction - Other Intangible

Introduction - Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Other intangible assets subject to amortization:
Gross Carrying Amount	$ 761	$ 773
Accumulated Amortization	(251)	(235)
Other Intangible Assets, Net	510	538
Other intangible assets not subject to amortization:
Federal Communications Commission licenses	75	75
Total other intangible assets
Gross Carrying Amount	836	848
Other Intangible Assets, Net	585	613
Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	211	223
Accumulated Amortization	(100)	(94)
Other Intangible Assets, Net	111	129
Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	70	70
Accumulated Amortization	(22)	(21)
Other Intangible Assets, Net	48	49
Other
Other intangible assets subject to amortization:
Gross Carrying Amount	11	11
Accumulated Amortization	(6)	(5)
Other Intangible Assets, Net	5	6
SOUTHERN POWER CO
Other intangible assets subject to amortization:
Accumulated Amortization	(67)	(61)
SOUTHERN POWER CO | PPA fair value adjustments
Other intangible assets subject to amortization:
Gross Carrying Amount	405	405
Accumulated Amortization	(67)	(61)
Other Intangible Assets, Net	338	344
SOUTHERN Co GAS
Other intangible assets subject to amortization:
Gross Carrying Amount	246	246
Accumulated Amortization	(153)	(145)
Other Intangible Assets, Net	93	101
Total other intangible assets
Other Intangible Assets, Net	93	101
SOUTHERN Co GAS | Customer relationships
Other intangible assets subject to amortization:
Gross Carrying Amount	156	156
Accumulated Amortization	(89)	(84)
Other Intangible Assets, Net	67	72
SOUTHERN Co GAS | Trade names
Other intangible assets subject to amortization:
Gross Carrying Amount	26	26
Accumulated Amortization	(8)	(7)
Other Intangible Assets, Net	18	19
SOUTHERN Co GAS | Storage and transportation contracts
Other intangible assets subject to amortization:
Gross Carrying Amount	64	64
Accumulated Amortization	(56)	(54)
Other Intangible Assets, Net	$ 8	$ 10

Introduction - Intangibles, Amo

Introduction - Intangibles, Amortization (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 17
SOUTHERN POWER CO
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	6
SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	8
Gas Marketing Services | SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	6
Wholesale Gas Services | SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 2

Introduction - Restricted Cash

Introduction - Restricted Cash (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 1,361	$ 1,396
Cash and cash equivalents held for sale		9
Restricted cash:
Total cash, cash equivalents, and restricted cash	1,364	1,519	$ 2,290	$ 2,147
Restricted cash
Restricted cash:
Restricted cash		0
Other accounts and notes receivable
Restricted cash:
Restricted cash	4	114
GEORGIA POWER CO
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	9	4
Cash and cash equivalents held for sale		0
Restricted cash:
Total cash, cash equivalents, and restricted cash	9	112	1,158	852
GEORGIA POWER CO | Restricted cash
Restricted cash:
Restricted cash		108
GEORGIA POWER CO | Other accounts and notes receivable
Restricted cash:
Restricted cash		0
SOUTHERN Co GAS
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	57	64
Cash and cash equivalents held for sale		0
Restricted cash:
Total cash, cash equivalents, and restricted cash	61	70	$ 100	$ 78
SOUTHERN Co GAS | Restricted cash
Restricted cash:
Restricted cash		0
SOUTHERN Co GAS | Other accounts and notes receivable
Restricted cash:
Restricted cash	$ 4	$ 6

Regulatory Matters - Cost Recov

Regulatory Matters - Cost Recovery Clauses (Details) - USD ($) $ in Millions	Mar. 31, 2019	Feb. 05, 2019	Dec. 31, 2018
ALABAMA POWER CO
Loss Contingencies [Line Items]
Rate RSE Refund Liability		$ 75
ALABAMA POWER CO | Deferred under recovered regulatory clause revenues
Loss Contingencies [Line Items]
Rate CNP Compliance	$ 0		$ 42
Rate CNP PPA	21		25
Retail Energy Cost Recovery()	0		109
ALABAMA POWER CO | Customer accounts receivable
Loss Contingencies [Line Items]
Rate CNP Compliance	25		0
ALABAMA POWER CO | Other regulatory liabilities, deferred
Loss Contingencies [Line Items]
Retail Energy Cost Recovery()	2		0
Natural Disaster Reserve	22		20
GEORGIA POWER CO | Receivables – under recovered fuel clause revenues
Loss Contingencies [Line Items]
Fuel Cost Recovery	73		115
MISSISSIPPI POWER CO | Over recovered retail fuel costs
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ 10		$ 8

Regulatory Matters - Alabama Po

Regulatory Matters - Alabama Power (Details) - USD ($) $ in Millions	Apr. 15, 2019	Mar. 31, 2019	Feb. 28, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Plant in service, net of depreciation		$ (71,839)		$ (72,668)
Other utility plant, net		1,315		0
ALABAMA POWER CO
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Plant in service, net of depreciation		(19,363)		(20,414)
Other utility plant, net		$ 1,315		$ 0
ALABAMA POWER CO | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Plant in service, net of depreciation			$ 1,300
Other utility plant, net			$ 1,300
ALABAMA POWER CO | Subsequent Event | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Capitalized asset retirement costs, net	$ 700
Regulatory asset to be recovered over the units' remaining useful lives	700
ALABAMA POWER CO | Plant Gorgas Units 8, 9, and 10 | Subsequent Event | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net investment costs	740
Regulatory asset to be recovered over the units' remaining useful lives	$ 740

Regulatory Matters - Nuclear Co

Regulatory Matters - Nuclear Construction (Details) - GEORGIA POWER CO $ in Millions

Jan. 01, 2021

Jan. 01, 2020

Feb. 19, 2019USD ($)

Jan. 11, 2018USD ($)

Jan. 01, 2016

Dec. 31, 2018USD ($)appeal

Aug. 31, 2018USD ($)

Mar. 31, 2019USD ($)

Dec. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2009USD ($)utilityMW

Dec. 31, 2022USD ($)

Dec. 31, 2014

Dec. 31, 2013

Loss Contingencies [Line Items]

Number of construction units approved | utility

2

Electric generating capacity in mega watts under consortium agreement | MW

1,100

Additional construction capital costs

$ 3,300

Estimated in-service capital cost

$ 4,418

Financing costs collected, net of tax

$ 1,900

Increase in NCCR tariff

$ 88

Amendment to estimated in-service capital cost

$ 5,680

Retail rate of return on common equity

10.95%

Number of appeals | appeal

2

Requested capital construction costs

$ 5,400

Deferred approval of expenditures related to administrative claim

$ 51.6

FFB Loan

Loss Contingencies [Line Items]

Long-term line of credit

3,460

Eligible project costs to be reimbursed

$ 5,130

Plant Vogtle Units 3 And 4

Loss Contingencies [Line Items]

Proportionate ownership share

45.70%

Construction financing costs

$ 1,900

Base project capital cost forecast, monthly

50

Monthly AFUDC

12

Percentage of ownership interest required for voting for continuing construction

90.00%

90.00%

Cost settlement agreement revised forecast, net of payments

$ 7,300

Public utilities, approved return on equity percentage

10.00%

Public utilities, approved return on equity, monthly percentage decrease

0.10%

Return on equity reduction, negative impact on earnings

$ 100

Requested capital construction costs

$ 578

Guarantor obligations

$ 1,700

Customer refund

$ 188

Plant Vogtle Units 3 And 4 | Scenario, Forecast

Loss Contingencies [Line Items]

Construction financing costs

$ 3,100

Public utilities, approved return on equity percentage

5.30%

8.30%

Return on equity reduction, negative impact on earnings

$ 75

$ 635

Plant Vogtle Units 3 And 4 | Vogtle Owners

Loss Contingencies [Line Items]

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

30 days

Regulatory Matters - Nuclear _2

Regulatory Matters - Nuclear Construction Cost and Schedule (Details) - GEORGIA POWER CO - Plant Vogtle Units 3 And 4 $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Loss Contingencies [Line Items]
Base project capital cost forecast	$ 8,000
Construction contingency estimate	400
Total project capital cost forecast	8,400
Net investment as of March 31, 2019	(4,900)
Remaining estimate to complete	3,500
Expected capitalized costs	325
Guarantor obligations	1,700
Customer refund	$ 188

Regulatory Matters - Mississipp

Regulatory Matters - Mississippi Power (Details) $ in Millions	Mar. 28, 2019USD ($)
MRA Revenue | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Decrease in base rate under cost based electric tariff	$ 3.7

Regulatory Matters - Kemper Cou

Regulatory Matters - Kemper County Energy Facility (Details) - MISSISSIPPI POWER CO - Kemper IGCC - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended	48 Months Ended
	Dec. 31, 2018	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2023
Loss Contingencies [Line Items]
Pre-tax charge to income		$ 2
Asset retirement obligation, liabilities incurred, net of tax		1
Asset retirement obligation, expected cost		$ 10
Government grants received	$ 387
Scenario, Forecast
Loss Contingencies [Line Items]
Asset retirement obligation, liabilities incurred			$ 11
Minimum | Scenario, Forecast
Loss Contingencies [Line Items]
Asset retirement obligation, liabilities incurred				$ 2
Maximum | Scenario, Forecast
Loss Contingencies [Line Items]
Asset retirement obligation, liabilities incurred				$ 6

Regulatory Matters - Southern C

Regulatory Matters - Southern Company Gas (Details) $ in Millions	Apr. 16, 2019USD ($)intervenor	Apr. 08, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Nov. 30, 2018USD ($)	Dec. 31, 2018
Nicor Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount					$ 230
Public utilities, approved return on equity percentage					10.60%
Regulatory equity ratio					54.00%	52.00%
Virginia Natural Gas
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount				$ (14)
Bill credits			$ 14
Subsequent Event | Nicor Gas
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage	9.86%
Regulatory equity ratio	54.00%
Number of intervenors | intervenor	2
Requested increase in rate amounts	$ 180
Subsequent Event | SAVE | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		$ 370
Infrastructure replacement program, petitioned investment renewal term		5 years
Infrastructure replacement program, petitioned investment term		6 years
Infrastructure replacement program, proposed investment variance amount		$ 10
Subsequent Event | SAVE | 2018 | Virginia Natural Gas
Loss Contingencies [Line Items]
Approved investment amount		35
Subsequent Event | SAVE | 2019 | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		40
Infrastructure replacement program, proposed investment variance amount		6
Subsequent Event | SAVE | 2020 | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		50
Infrastructure replacement program, proposed investment variance amount		8
Subsequent Event | SAVE | 2021 | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		60
Infrastructure replacement program, proposed investment variance amount		9
Subsequent Event | SAVE | 2022 | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		70
Infrastructure replacement program, proposed investment variance amount		10
Subsequent Event | SAVE | 2023 | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		70
Infrastructure replacement program, proposed investment variance amount		10
Subsequent Event | SAVE | 2024 | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, proposed investment amount		70
Infrastructure replacement program, proposed investment variance amount		$ 10

Regulatory Matters - FERC Matte

Regulatory Matters - FERC Matters (Details) - Open Access Transmission Tariff - SCS	May 10, 2018
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage	10.60%
Moratorium period	5 years

Contingencies - General Litigat

Contingencies - General Litigation Matters (Details) $ in Millions	1 Months Ended				3 Months Ended	12 Months Ended
	May 31, 2019USD ($)	Nov. 30, 2018defendantplaintiff	May 31, 2018USD ($)agreement	Apr. 30, 2018	Mar. 31, 2019USD ($)	Dec. 31, 2017claim
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff		10
Pending Litigation | Putative Securities Class Action
Loss Contingencies [Line Items]
Increase in the purported class period						1 day
Pending Litigation | Shareholder Derivative Lawsuits
Loss Contingencies [Line Items]
Pending number of claims | claim						2
Stay period			30 days	30 days
MISSISSIPPI POWER CO | Pending Litigation | Martin Product Sales, LLC Litigation
Loss Contingencies [Line Items]
Number of agreements | agreement			2
MISSISSIPPI POWER CO | Pending Litigation | Purported Violations Of Mississippi Consumer Protection Act
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff		4
Number of defendants | defendant		3
Martin Product Sales, LLC Litigation | Martin Product Sales, LLC Litigation
Loss Contingencies [Line Items]
Damages sought by litigation			$ 143
SOUTHERN POWER CO
Loss Contingencies [Line Items]
Withholding of construction contract payments					$ 26
SOUTHERN POWER CO | RE Roserock, LLC | RE Roserock, LLC
Loss Contingencies [Line Items]
Ownership percentage by parent					51.00%
RE Roserock, LLC
Loss Contingencies [Line Items]
Insurance proceeds					$ 5
RE Roserock, LLC | Scenario, Forecast | Subsequent Event
Loss Contingencies [Line Items]
Amount paid to other party	$ 26

Contingencies - Environmental R

Contingencies - Environmental Remediation (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 18	$ 23
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	289	$ 294
Location One | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability, current and former sites	$ 2

Contingencies - Other Matters (

Contingencies - Other Matters (Details) - Subsequent Event - Scenario, Forecast - Plant Daniel Units 1 And 2	60 Months Ended
	Jan. 15, 2024USD ($)
GULF POWER CO
Loss Contingencies [Line Items]
Undivided ownership interest to be sold	50.00%
Undivided ownership interest, ownership interest in individual unit	100.00%
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Payments to acquire business	$ 1
Option to purchase, period	120 days

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 5,412	$ 6,372
Revenue from leases	139
Total retail electric and gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4,245	4,768
Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from leases	8	18
Increase (decrease) in revenue from cost recovery mechanisms	(103)	117
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	1,288	1,539
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,093	1,243
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	677	756
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	26	30
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,163	1,224
Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues	(2)	(24)
Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	367	472
Revenue from leases	66	69
Revenue from transactions accounted for as derivatives	53	93
Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	132	151
Revenue from leases	25	30
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	313	407
Revenue from leases	9
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	355	574
Revenue from leases	31	33
Revenues not accounted for under ASC 606	96	90
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,408	1,473
ALABAMA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,213	1,285
Increase (decrease) in revenue from cost recovery mechanisms	(57)	47
ALABAMA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	540	570
ALABAMA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	354	371
ALABAMA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	313	338
ALABAMA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	6	6
ALABAMA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	94	101
Revenue from transactions accounted for as derivatives	3	5
ALABAMA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	27	24
ALABAMA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	74	63
Revenues not accounted for under ASC 606	28	25
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,833	1,961
Revenue from leases	19
GEORGIA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,668	1,798
Revenue from leases	8	18
Increase (decrease) in revenue from cost recovery mechanisms	(47)	10
GEORGIA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	688	744
GEORGIA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	674	717
GEORGIA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	289	316
GEORGIA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	17	21
GEORGIA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	18	40
Revenue from transactions accounted for as derivatives	4	7
GEORGIA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	14	14
GEORGIA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	133	109
Revenue from leases	11	33
Revenues not accounted for under ASC 606	31	26
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	287	302
Revenue from leases	2
MISSISSIPPI POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	203	194
Increase (decrease) in revenue from cost recovery mechanisms	1	76
MISSISSIPPI POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	60	60
MISSISSIPPI POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	65	62
MISSISSIPPI POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	74	70
MISSISSIPPI POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	4	2
MISSISSIPPI POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	78	98
Revenue from transactions accounted for as derivatives	1	1
MISSISSIPPI POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1	4
MISSISSIPPI POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	5	6
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	443	509
Revenue from leases	113
SOUTHERN POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	127	138
Revenue from leases	41	47
SOUTHERN POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	227	254
Revenue from leases	72	76
SOUTHERN POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	85	115
Revenue from transactions accounted for as derivatives	45	79
SOUTHERN POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4	2
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,474	1,639
Revenue from leases	9
SOUTHERN Co GAS | Wholesale Gas Services | Third Party Gross Revenues
Disaggregation of Revenue [Line Items]
Revenue from transactions accounted for as derivatives	1,200	1,100
SOUTHERN Co GAS | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,161	1,200
SOUTHERN Co GAS | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	601	660
SOUTHERN Co GAS | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	170	192
SOUTHERN Co GAS | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	256	277
SOUTHERN Co GAS | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	17	17
SOUTHERN Co GAS | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	119	78
SOUTHERN Co GAS | Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues	(2)	(24)
SOUTHERN Co GAS | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	8	8
Revenue from leases	8
SOUTHERN Co GAS | Wholesale Gas Services
Disaggregation of Revenue [Line Items]
Total operating revenues	66	146
SOUTHERN Co GAS | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	229	271
Revenues not accounted for under ASC 606	6	4
SOUTHERN Co GAS | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	10	14
Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,495	1,657
Operating Segments | SOUTHERN Co GAS | Wholesale Gas Services
Disaggregation of Revenue [Line Items]
Total operating revenues	86	166
Operating Segments | SOUTHERN Co GAS | Wholesale Gas Services | Third Party Gross Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,926	$ 1,938

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Receivables	$ 2,522	$ 2,630
Contract Assets	84	102
Contract Liabilities	62	32
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Receivables	514	520
Contract Assets	1	0
Contract Liabilities	10	12
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Receivables	668	721
Contract Assets	41	58
Contract Liabilities	25	7
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Receivables	85	100
Contract Assets	0	0
Contract Liabilities	0	0
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Receivables	99	118
Contract Assets	0	0
Contract Liabilities	4	11
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Receivables	948	952
Contract Assets	0	0
Contract Liabilities	$ 1	$ 2

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Contract assets	$ 84	$ 102
Contract liabilities	62	32
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract assets	34	39
Contract liabilities	$ 25	11
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Performance obligation, expected timing of satisfaction	Georgia Power had contract assets primarily related to unregulated service agreements where payment is contingent on project completion and fixed retail customer bill programs where the payment is contingent upon Georgia Power's continued performance and the customer's continued participation in the program over the one-year contract term.
Contract assets	$ 41	58
Contract liabilities	$ 25	$ 7

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Revenue from Contracts with Customers (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers recognized	$ 17
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers recognized	$ 10

Revenue from Contracts with C_7

Revenue from Contracts with Customers - Performance Obligations (Details) $ in Millions	Mar. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 451
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 349
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 315
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 310
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 301
Performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2,219
Performance obligation, expected timing of satisfaction
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 16
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 22
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 27
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 23
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 22
Performance obligation, expected timing of satisfaction	1 year
ALABAMA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 140
Performance obligation, expected timing of satisfaction
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 30
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 38
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 40
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 30
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 31
Performance obligation, expected timing of satisfaction	1 year
GEORGIA POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 82
Performance obligation, expected timing of satisfaction
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 3
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 1
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction	1 year
MISSISSIPPI POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 0
Performance obligation, expected timing of satisfaction
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 248
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 295
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 270
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 276
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 269
Performance obligation, expected timing of satisfaction	1 year
SOUTHERN POWER CO | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 2,143
Performance obligation, expected timing of satisfaction

Consolidated Entities and Equ_3

Consolidated Entities and Equity Method Investments - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)investor
SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	67.00%
Global Atlantic
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	33.00%
SP Solar Holdings I, LP | Variable Interest Entity, Primary Beneficiary | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 6,500
Liabilities	373
Noncontrolling interests related to other partners' interests	$ 1,200
SP Wind | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	60.00%
Number of financial investors | investor	3
SP Wind | Financial Investors
Schedule of Equity Method Investments [Line Items]
Distribution made to limited partner, cash distributions paid, percentage	40.00%
SP Wind | Variable Interest Entity, Primary Beneficiary | SOUTHERN POWER CO
Schedule of Equity Method Investments [Line Items]
Assets	$ 2,600
Liabilities	141
Noncontrolling interests related to other partners' interests	$ 46

Consolidated Entities and Equ_4

Consolidated Entities and Equity Method Investments - Balance Sheet Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 1,598	$ 1,580
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,557	1,538
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Investment Balance	1,262	1,261
SOUTHERN Co GAS | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Investment Balance	96	83
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Investment Balance	75	71
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Investment Balance	$ 124	$ 123

Consolidated Entities and Equ_5

Consolidated Entities and Equity Method Investments - Income Statement Equity Method Investment Carrying Amount (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	$ 48	$ 41
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	48	42
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	42	39
SOUTHERN Co GAS | Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	3	1
SOUTHERN Co GAS | PennEast Pipeline
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	2	1
SOUTHERN Co GAS | Other
Schedule of Equity Method Investments [Line Items]
Earnings from Equity Method Investments	$ 1	$ 1

Consolidated Entities and Equ_6

Consolidated Entities and Equity Method Investments - Investment in SNG (Details) - SNG - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement Information
Revenues	$ 166	$ 160
Operating income	106	99
Net income	$ 84	$ 78

Financing - Narrative (Details)

Financing - Narrative (Details) shares in Millions	1 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)	Jan. 31, 2019USD ($)	Mar. 31, 2019USD ($)loanshares	Mar. 31, 2018USD ($)shares	Dec. 31, 2014	Apr. 30, 2019USD ($)	Aug. 31, 2018
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	$ 1,400,000,000		$ 1,400,000,000
Maximum borrowing capacity	7,863,000,000		7,863,000,000
Repayments of short-term debt			$ 1,750,000,000	$ 150,000,000
Stock-based compensation awards not included in the diluted earnings per share calculation because they were anti-dilutive (in shares) | shares			0	0
Senior Notes
Debt Instrument [Line Items]
Repayments of debt		$ 1,200,000,000
Senior Notes | 1.85% Notes
Debt Instrument [Line Items]
Interest rate		1.85%
Repurchase amount		$ 522,000,000
Debt face amount		$ 1,000,000,000
Senior Notes | Series 2014B Notes
Debt Instrument [Line Items]
Interest rate		2.15%
Repurchase amount		$ 180,000,000
Debt face amount		350,000,000
Senior Notes | Series 2018A Notes
Debt Instrument [Line Items]
Repurchase amount		504,000,000
Debt face amount		750,000,000
Notes Payable to Banks | Uncommitted Bank Credit Arrangement
Debt Instrument [Line Items]
Repayments of short-term debt		250,000,000
Notes Payable to Banks | Floating Rate Bank Term Loan Agreement
Debt Instrument [Line Items]
Repayments of short-term debt		1,500,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	854,000,000		$ 854,000,000
Fixed rate pollution control revenue bonds outstanding	87,000,000		87,000,000
Maximum borrowing capacity	1,333,000,000		1,333,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	550,000,000		550,000,000
Fixed rate pollution control revenue bonds outstanding	345,000,000		345,000,000
Maximum borrowing capacity	1,750,000,000		1,750,000,000
Repayments of short-term debt			0	$ 150,000,000
GEORGIA POWER CO | Subsequent Event
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding						$ 115,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project) First Series 1992
Debt Instrument [Line Items]
Redeemed aggregate principal amount		13,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Eighth Series 1994
Debt Instrument [Line Items]
Redeemed aggregate principal amount		20,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 1995
Debt Instrument [Line Items]
Redeemed aggregate principal amount		$ 75,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 2009
Debt Instrument [Line Items]
Debt face amount	173,000,000		173,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2013
Debt Instrument [Line Items]
Debt face amount	105,000,000		105,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 2008
Debt Instrument [Line Items]
Debt face amount	65,000,000		$ 65,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fourth Series 1994 | Subsequent Event
Debt Instrument [Line Items]
Debt face amount						55,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fourth Series 1995 | Subsequent Event
Debt Instrument [Line Items]
Debt face amount						30,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Ninth Series 1994 | Subsequent Event
Debt Instrument [Line Items]
Debt face amount						20,000,000
GEORGIA POWER CO | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 1994 | Subsequent Event
Debt Instrument [Line Items]
Debt face amount						$ 10,000,000
GEORGIA POWER CO | Plant Vogtle Units 3 And 4
Debt Instrument [Line Items]
Undivided ownership interest					45.70%
GEORGIA POWER CO | Term Loan
Debt Instrument [Line Items]
Number of term loan facilities | loan			2
GEORGIA POWER CO | 2014 FFB Credit Facility
Debt Instrument [Line Items]
Eligible project costs to be reimbursed			$ 5,130,000,000
Eligible project costs to be reimbursed, percentage					70.00%
Borrowings made	$ 835,000,000
Interest rate	3.213%		3.213%
Borrowings outstanding	$ 3,460,000,000		$ 3,460,000,000
Amortization period for line of credit facility					5 years
GEORGIA POWER CO | 2014 FFB Credit Facility | U.S. Treasury Rate
Debt Instrument [Line Items]
Basis spread					0.375%
GEORGIA POWER CO | Additional FFB Credit Facility
Debt Instrument [Line Items]
Eligible project costs to be reimbursed, percentage	70.00%
Amounts received under Guarantee Settlement Agreement, less Custumer Refunds	$ 1,492,000,000		1,492,000,000
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	40,000,000		40,000,000
Maximum borrowing capacity	100,000,000		100,000,000
MISSISSIPPI POWER CO | Municipal bonds | Mississippi Business Finance Corporation Pollution Control Revenue Refunding Bonds, Series 2002
Debt Instrument [Line Items]
Debt face amount	43,000,000		43,000,000
Traditional Electric Operating Companies
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding	432,000,000		432,000,000
SOUTHERN POWER CO
Debt Instrument [Line Items]
Maximum borrowing capacity	750,000,000		750,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Maximum borrowing capacity	1,900,000,000		1,900,000,000
Nicor Gas
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 500,000,000		$ 500,000,000
Plant Vogtle Units 3 And 4 | GEORGIA POWER CO
Debt Instrument [Line Items]
Undivided ownership interest	45.70%		45.70%
Failure to vote, percentage of ownership interests					90.00%		90.00%

Financing - Schedule of Credit

Financing - Schedule of Credit Arrangements (Details)	Mar. 31, 2019USD ($)
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	7,834,000,000
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
ALABAMA POWER CO
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
GEORGIA POWER CO
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
MISSISSIPPI POWER CO
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
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
Expires, 2019	0
Expires, 2020	0
Expires, 2022	750,000,000
Total	750,000,000
Unused	741,000,000
SOUTHERN POWER CO | Standby Letters of Credit
Line of Credit Facility [Line Items]
Total	120,000,000
Unused	24,000,000
SOUTHERN Co 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
Other
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
Southern Company Gas Capital
Line of Credit Facility [Line Items]
Total	1,400,000,000
Nicor Gas
Line of Credit Facility [Line Items]
Total	$ 500,000,000

Financing - Schedule of Long-Te

Financing - Schedule of Long-Term Debt Financing Activities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Debt Instrument [Line Items]
Senior Note Maturities, Redemptions, and Repurchases	$ 2,300
Revenue Bond Issuances and Reofferings of Purchased Bonds	386
Revenue Bond Maturities, Redemptions, and Repurchases	108
Other Long-Term Debt Issuances	835
Other Long-Term Debt Redemptions and Maturities	21
Southern Company
Debt Instrument [Line Items]
Senior Note Maturities, Redemptions, and Repurchases	2,100
Revenue Bond Issuances and Reofferings of Purchased Bonds	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	0
ALABAMA POWER CO
Debt Instrument [Line Items]
Senior Note Maturities, Redemptions, and Repurchases	200
Revenue Bond Issuances and Reofferings of Purchased Bonds	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	0
GEORGIA POWER CO
Debt Instrument [Line Items]
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Issuances and Reofferings of Purchased Bonds	343
Revenue Bond Maturities, Redemptions, and Repurchases	108
Other Long-Term Debt Issuances	835
Other Long-Term Debt Redemptions and Maturities	2
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Issuances and Reofferings of Purchased Bonds	43
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	0
Other
Debt Instrument [Line Items]
Senior Note Maturities, Redemptions, and Repurchases	0
Revenue Bond Issuances and Reofferings of Purchased Bonds	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	$ 19

Financing - Shares Used to Comp

Financing - Shares Used to Compute Diluted Earnings Per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Debt Disclosure [Abstract]
As reported shares	1,038	1,011
Effect of stock-based compensation	7	5
Diluted shares	1,045	1,016

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	39.80%	10.80%
ALABAMA POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	21.90%	26.30%
MISSISSIPPI POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	15.50%	(34.70%)
SOUTHERN POWER CO
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	(49.80%)	(647.00%)
SOUTHERN Co GAS
Income Tax Contingency [Line Items]
Effective tax (benefit) rate	22.30%	27.20%

Retirement Benefits (Details)

Retirement Benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Amortization:
Net (gain)/loss
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, remainder of fiscal year	$ 0
Pension Plans | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	17,000,000	19,000,000
Interest cost	28,000,000	25,000,000
Expected return on plan assets	(51,000,000)	(51,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	9,000,000	14,000,000
Net periodic pension cost (income)	3,000,000	7,000,000
Pension Plans | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	19,000,000	22,000,000
Interest cost	39,000,000	35,000,000
Expected return on plan assets	(73,000,000)	(74,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	11,000,000	17,000,000
Net periodic pension cost (income)	(4,000,000)	0
Pension Plans | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	3,000,000	4,000,000
Interest cost	6,000,000	5,000,000
Expected return on plan assets	(10,000,000)	(10,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	1,000,000	3,000,000
Net periodic pension cost (income)	0	2,000,000
Pension Plans | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	2,000,000	2,000,000
Interest cost	1,000,000	1,000,000
Expected return on plan assets	(2,000,000)	(3,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	0	1,000,000
Net periodic pension cost (income)	1,000,000	1,000,000
Pension Plans | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	6,000,000	8,000,000
Interest cost	9,000,000	10,000,000
Expected return on plan assets	(15,000,000)	(18,000,000)
Amortization:
Prior service costs	(1,000,000)	(1,000,000)
Regulatory asset	3,000,000	3,000,000
Net (gain)/loss	1,000,000	3,000,000
Net periodic pension cost (income)	3,000,000	5,000,000
Pension Plans | Southern Company
Pension Plans and Postretirement Plans
Service cost	73,000,000	90,000,000
Interest cost	123,000,000	116,000,000
Expected return on plan assets	(221,000,000)	(236,000,000)
Amortization:
Prior service costs	0	1,000,000
Regulatory asset	0	0
Net (gain)/loss	30,000,000	53,000,000
Net periodic pension cost (income)	5,000,000	24,000,000
Postretirement Benefits | ALABAMA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	4,000,000	4,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	1,000,000	1,000,000
Regulatory asset	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	0	0
Postretirement Benefits | GEORGIA POWER CO
Pension Plans and Postretirement Plans
Service cost	1,000,000	2,000,000
Interest cost	7,000,000	7,000,000
Expected return on plan assets	(6,000,000)	(6,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	0	2,000,000
Net periodic pension cost (income)	2,000,000	5,000,000
Postretirement Benefits | MISSISSIPPI POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	1,000,000	1,000,000
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	1,000,000	1,000,000
Postretirement Benefits | SOUTHERN POWER CO
Pension Plans and Postretirement Plans
Service cost	0	0
Interest cost	0	0
Expected return on plan assets	0	0
Amortization:
Prior service costs	0	0
Regulatory asset	0	0
Net (gain)/loss	0	0
Net periodic pension cost (income)	0	0
Postretirement Benefits | SOUTHERN Co GAS
Pension Plans and Postretirement Plans
Service cost	1,000,000	1,000,000
Interest cost	2,000,000	2,000,000
Expected return on plan assets	(2,000,000)	(2,000,000)
Amortization:
Prior service costs	0	0
Regulatory asset	2,000,000	1,000,000
Net (gain)/loss	(1,000,000)	0
Net periodic pension cost (income)	2,000,000	2,000,000
Postretirement Benefits | Southern Company
Pension Plans and Postretirement Plans
Service cost	5,000,000	6,000,000
Interest cost	17,000,000	19,000,000
Expected return on plan assets	(16,000,000)	(17,000,000)
Amortization:
Prior service costs	1,000,000	2,000,000
Regulatory asset	0	0
Net (gain)/loss	(1,000,000)	3,000,000
Net periodic pension cost (income)	$ 6,000,000	$ 13,000,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets:
Derivatives	$ 159	$ 313
Liabilities:
Derivatives	131	235
Collateral already posted, aggregate fair value	190
ALABAMA POWER CO
Assets:
Derivatives	1	2
Liabilities:
Derivatives	2	6
GEORGIA POWER CO
Assets:
Derivatives	1	0
Investments in trusts	72
Liabilities:
Derivatives	10	17
MISSISSIPPI POWER CO
Assets:
Derivatives	0	1
Liabilities:
Derivatives	3	7
SOUTHERN POWER CO
Assets:
Derivatives	38	76
Liabilities:
Derivatives	26	28
SOUTHERN Co GAS
Assets:
Derivatives	118	233
Liabilities:
Derivatives	56	124
Collateral already posted, aggregate fair value	190	$ 277
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	910
Other investments	23
Total	3,327
Liabilities:
Contingent consideration	21
Total	675
Fair Value, Measurements, Recurring | Weather Derivative
Liabilities:
Derivatives	11
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	907
Other investments	9
Total	2,033
Liabilities:
Contingent consideration	0
Total	466
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	3
Other investments	14
Total	1,242
Liabilities:
Contingent consideration	0
Total	165
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Other investments	0
Total	4
Liabilities:
Contingent consideration	21
Total	44
Fair Value, Measurements, Recurring | Net Asset Value as a Practical Expedient (NAV)
Assets:
Total	48
Fair Value, Measurements, Recurring | Energy-related derivatives
Assets:
Derivatives	454
Liabilities:
Derivatives	595
Fair Value, Measurements, Recurring | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	322
Liabilities:
Derivatives	466
Fair Value, Measurements, Recurring | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	128
Liabilities:
Derivatives	106
Fair Value, Measurements, Recurring | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	4
Liabilities:
Derivatives	23
Fair Value, Measurements, Recurring | Interest rate derivatives
Liabilities:
Derivatives	35
Fair Value, Measurements, Recurring | Interest rate derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | Interest rate derivatives | Significant Other Observable Inputs (Level 2)
Liabilities:
Derivatives	35
Fair Value, Measurements, Recurring | Interest rate derivatives | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | Foreign currency derivatives
Assets:
Derivatives	38
Liabilities:
Derivatives	24
Fair Value, Measurements, Recurring | Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | Foreign currency derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	38
Liabilities:
Derivatives	24
Fair Value, Measurements, Recurring | Foreign currency derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | Domestic equity
Assets:
Investments in trusts	802
Fair Value, Measurements, Recurring | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	682
Fair Value, Measurements, Recurring | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	120
Fair Value, Measurements, Recurring | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Foreign equity
Assets:
Investments in trusts	255
Fair Value, Measurements, Recurring | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	60
Fair Value, Measurements, Recurring | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	195
Fair Value, Measurements, Recurring | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities
Assets:
Investments in trusts	283
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	283
Fair Value, Measurements, Recurring | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Municipal bonds
Assets:
Investments in trusts	73
Fair Value, Measurements, Recurring | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Municipal bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	73
Fair Value, Measurements, Recurring | Municipal bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Pooled funds – fixed income
Assets:
Investments in trusts	14
Fair Value, Measurements, Recurring | Pooled funds – fixed income | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Pooled funds – fixed income | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	14
Fair Value, Measurements, Recurring | Pooled funds – fixed income | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Corporate bonds
Assets:
Investments in trusts	322
Fair Value, Measurements, Recurring | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	24
Fair Value, Measurements, Recurring | Corporate bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	298
Fair Value, Measurements, Recurring | Corporate bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Mortgage and asset backed securities
Assets:
Investments in trusts	72
Fair Value, Measurements, Recurring | Mortgage and asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Mortgage and asset backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	72
Fair Value, Measurements, Recurring | Mortgage and asset backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity
Assets:
Investments in trusts	48
Fair Value, Measurements, Recurring | Private equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Private equity | Net Asset Value as a Practical Expedient (NAV)
Assets:
Investments in trusts	48
Fair Value, Measurements, Recurring | Cash and cash equivalents
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | Cash and cash equivalents | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Cash and cash equivalents | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | Other
Assets:
Investments in trusts	32
Fair Value, Measurements, Recurring | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	28
Fair Value, Measurements, Recurring | Other | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	4
Fair Value, Measurements, Recurring | Other | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO
Assets:
Cash equivalents	572
Other investments	14
Total	1,522
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	569
Other investments	0
Total	1,104
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	3
Other investments	14
Total	370
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Other investments	0
Total	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Net Asset Value as a Practical Expedient (NAV)
Assets:
Total	48
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives
Assets:
Derivatives	6
Liabilities:
Derivatives	7
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	6
Liabilities:
Derivatives	7
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity
Assets:
Investments in trusts	554
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	446
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	108
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity
Assets:
Investments in trusts	117
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	60
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	57
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities
Assets:
Investments in trusts	18
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	18
Fair Value, Measurements, Recurring | ALABAMA POWER CO | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds
Assets:
Investments in trusts	163
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	24
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	139
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Corporate bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities
Assets:
Investments in trusts	24
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	24
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Mortgage and asset backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity
Assets:
Investments in trusts	48
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Private equity | Net Asset Value as a Practical Expedient (NAV)
Assets:
Investments in trusts	48
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other
Assets:
Investments in trusts	5
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	5
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | ALABAMA POWER CO | Other | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO
Assets:
Total	951
Liabilities:
Total	18
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	259
Liabilities:
Total	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Total	692
Liabilities:
Total	18
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Total	0
Liabilities:
Total	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives
Assets:
Derivatives	9
Liabilities:
Derivatives	16
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	9
Liabilities:
Derivatives	16
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Interest rate derivatives
Liabilities:
Derivatives	2
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Interest rate derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Interest rate derivatives | Significant Other Observable Inputs (Level 2)
Liabilities:
Derivatives	2
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Interest rate derivatives | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity
Assets:
Investments in trusts	237
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	236
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	1
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity
Assets:
Investments in trusts	134
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	134
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities
Assets:
Investments in trusts	265
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	265
Fair Value, Measurements, Recurring | GEORGIA POWER CO | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds
Assets:
Investments in trusts	72
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	72
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds
Assets:
Investments in trusts	160
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	160
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Corporate bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities
Assets:
Investments in trusts	47
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	47
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Mortgage and asset backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other
Assets:
Investments in trusts	27
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Investments in trusts	23
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other | Significant Other Observable Inputs (Level 2)
Assets:
Investments in trusts	4
Fair Value, Measurements, Recurring | GEORGIA POWER CO | Other | Significant Unobservable Inputs (Level 3)
Assets:
Investments in trusts	0
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO
Assets:
Cash equivalents	202
Total	205
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	202
Total	202
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	3
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	0
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives
Assets:
Derivatives	3
Liabilities:
Derivatives	6
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	3
Liabilities:
Derivatives	6
Fair Value, Measurements, Recurring | MISSISSIPPI POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO
Assets:
Cash equivalents	10
Total	49
Liabilities:
Contingent consideration	21
Total	48
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	10
Total	10
Liabilities:
Contingent consideration	0
Total	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	39
Liabilities:
Contingent consideration	0
Total	27
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	0
Liabilities:
Contingent consideration	21
Total	21
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives
Assets:
Derivatives	1
Liabilities:
Derivatives	3
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	1
Liabilities:
Derivatives	3
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives
Assets:
Derivatives	38
Liabilities:
Derivatives	24
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	38
Liabilities:
Derivatives	24
Fair Value, Measurements, Recurring | SOUTHERN POWER CO | Foreign currency derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS
Assets:
Cash equivalents	13
Total	477
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	13
Total	336
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0
Total	137
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0
Total	4
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives
Assets:
Derivatives	434
Liabilities:
Derivatives	562
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivatives	322
Liabilities:
Derivatives	466
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivatives	108
Liabilities:
Derivatives	73
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Energy-related derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivatives	4
Liabilities:
Derivatives	23
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity
Assets:
Non-qualified deferred compensation trusts	11
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	11
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Domestic equity | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity
Assets:
Non-qualified deferred compensation trusts	4
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	4
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Foreign equity | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income
Assets:
Non-qualified deferred compensation trusts	14
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	14
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Pooled funds – fixed income | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Cash and cash equivalents
Assets:
Non-qualified deferred compensation trusts	1
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	1
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Cash and cash equivalents | Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	0
Fair Value, Measurements, Recurring | SOUTHERN Co GAS | Cash and cash equivalents | Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Increase (Decrease) In Fair Value Of Funds (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 152	$ (11)
ALABAMA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	87	(5)
GEORGIA POWER CO
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase (decrease) in fair value of funds	$ 65	$ (6)

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Millions	Mar. 31, 2019USD ($)$ / MMBTU	Dec. 31, 2018USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Derivatives	$ 131	$ 235
ALABAMA POWER CO
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Derivatives	2	6
ALABAMA POWER CO | Private equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value	48
Unfunded commitments	49
SOUTHERN Co GAS
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Derivatives	56	$ 124
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3) | Energy-related derivatives
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair value of derivatives	$ 19
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3) | Energy-related derivatives | Forward Price | Valuation, Market Approach | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Measurement input (usd per mmbtu) | $ / MMBTU	0.07
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3) | Energy-related derivatives | Forward Price | Valuation, Market Approach | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Measurement input (usd per mmbtu) | $ / MMBTU	1.15

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Mar. 31, 2019USD ($)
Long-term debt, including securities due within one year:
Carrying amount	$ 42,535
Fair value	43,910
ALABAMA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	7,921
Fair value	8,424
GEORGIA POWER CO
Long-term debt, including securities due within one year:
Carrying amount	10,910
Fair value	11,249
MISSISSIPPI POWER CO
Long-term debt, including securities due within one year:
Carrying amount	1,619
Fair value	1,619
SOUTHERN POWER CO
Long-term debt, including securities due within one year:
Carrying amount	4,995
Fair value	5,131
SOUTHERN Co GAS
Long-term debt, including securities due within one year:
Carrying amount	5,928
Fair value	$ 6,176

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value of Commodity Derivative Contracts that Include a Significant Unobservable Component (Details) - SOUTHERN Co GAS $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 0
Transfers to Level 3	(30)
Changes in fair value	11
Ending balance	$ (19)

Derivatives - Energy-Related an

Derivatives - Energy-Related and Interest Rate Derivatives (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2019USD ($)MMBTU
Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	538
Interest rate derivatives
Interest rate derivatives
Notional Amount | $	$ 2,000,000,000
Fair Value Gain (Loss) at March 31, 2019 | $	(35,000,000)
Southern Company | Interest rate derivatives | June 2020 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount | $	$ 300,000,000
Interest Rate Received	2.75%
Fair Value Gain (Loss) at March 31, 2019 | $	$ (3,000,000)
Southern Company | Interest rate derivatives | July 2021 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount | $	$ 1,500,000,000
Interest Rate Received	2.35%
Fair Value Gain (Loss) at March 31, 2019 | $	$ (30,000,000)
Southern Company | LIBOR | Interest rate derivatives | June 2020 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.92%
Southern Company | LIBOR | Interest rate derivatives | July 2021 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	0.87%
ALABAMA POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	72
GEORGIA POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	153
GEORGIA POWER CO | Interest rate derivatives | December 2019 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Notional Amount | $	$ 200,000,000
Interest Rate Received	4.25%
Fair Value Gain (Loss) at March 31, 2019 | $	$ (2,000,000)
GEORGIA POWER CO | LIBOR | Interest rate derivatives | December 2019 | Fair Value Hedges of Existing Debt
Interest rate derivatives
Weighted Average Interest Rate Paid	2.46%
MISSISSIPPI POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	61
SOUTHERN POWER CO | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	9
SOUTHERN Co GAS | Energy-related, Natural Gas
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	243
SOUTHERN Co GAS | Energy-related, Natural Gas | Derivatives not designated as hedging instruments | Long
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | MMBTU	3,800
SOUTHERN Co GAS | Energy-related, Natural Gas | Derivatives not designated as hedging instruments | Short
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume | MMBTU	3,600

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2019USD ($)MMBTU	Dec. 31, 2018USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	40
Cash flow hedge gain (loss) to be reclassified within twelve months	$ (19,000,000)
Collateral already posted, aggregate fair value	$ 190,000,000
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	6
Cash flow hedge gain (loss) to be reclassified within twelve months	$ 0
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	12
Cash flow hedge gain (loss) to be reclassified within twelve months	$ 0
MISSISSIPPI POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	5
Cash flow hedge gain (loss) to be reclassified within twelve months	$ 0
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	13
Cash flow hedge gain (loss) to be reclassified within twelve months	$ 0
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	(24,000,000)
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, aggregate fair value	0
SOUTHERN Co GAS
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0
Collateral already posted, aggregate fair value	$ 190,000,000	$ 277,000,000

Derivatives - Foreign Currency

Derivatives - Foreign Currency Derivatives (Details) - 3 months ended Mar. 31, 2019 - Cash Flow Hedges of Existing Debt - Foreign currency derivatives € in Millions, $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Pay Notional	$ 1,241
Receive Notional | €		€ 1,100
Fair Value Gain (Loss) at March 31, 2019	13
SOUTHERN POWER CO | June 2022
Derivative [Line Items]
Pay Notional	$ 677
Pay Rate	2.95%
Receive Notional | €		600
Receive Rate	1.00%
Fair Value Gain (Loss) at March 31, 2019	$ 2
SOUTHERN POWER CO | June 2026
Derivative [Line Items]
Pay Notional	$ 564
Pay Rate	3.78%
Receive Notional | €		€ 500
Receive Rate	1.85%
Fair Value Gain (Loss) at March 31, 2019	$ 11

Derivatives - Derivative Financ

Derivatives - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivatives, assets	$ 492	$ 837
Derivatives, liabilities	654	1,036
Derivative asset, Gross amounts offset	(333)	(524)
Derivative liability, Gross amounts offset	(523)	(801)
Derivative asset	159	313
Derivative liability	131	235
Collateral already posted, aggregate fair value	190
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives, assets	430	741
Derivatives, liabilities	560	900
Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	259	561
Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	291	575
Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	171	180
Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	269	325
Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges
Derivatives, Fair Value [Line Items]
Derivatives, assets	23	17
Derivatives, liabilities	31	55
Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	12	8
Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	10	23
Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	9
Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	21	26
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	39	79
Derivatives, liabilities	63	81
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	3
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	3	7
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	2
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	20	19
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	15	30
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	24	23
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	38	75
Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
ALABAMA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	6	6
Derivatives, liabilities	7	10
Derivative asset, Gross amounts offset	(5)	(4)
Derivative liability, Gross amounts offset	(5)	(4)
Derivative asset	1	2
Derivative liability	2	6
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	6	6
Derivatives, liabilities	7	10
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	3
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	4
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	3
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	6
GEORGIA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	6
Derivatives, liabilities	18	23
Derivative asset, Gross amounts offset	(8)	(6)
Derivative liability, Gross amounts offset	(8)	(6)
Derivative asset	1	0
Derivative liability	10	17
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	6
Derivatives, liabilities	16	21
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	2
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	8
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	4
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	11	13
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	2	2
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Interest rate derivatives | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	2
MISSISSIPPI POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	3
Derivatives, liabilities	6	9
Derivative asset, Gross amounts offset	(3)	(2)
Derivative liability, Gross amounts offset	(3)	(2)
Derivative asset	0	1
Derivative liability	3	7
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	3
Derivatives, liabilities	6	9
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	1
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	3
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	2
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	6
SOUTHERN POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	39	79
Derivatives, liabilities	27	31
Derivative asset, Gross amounts offset	(1)	(3)
Derivative liability, Gross amounts offset	(1)	(3)
Derivative asset	38	76
Derivative liability	26	28
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	39	79
Derivatives, liabilities	27	31
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	3
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	6
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	2
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Under recovered fuel balance
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	24	23
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	38	75
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Foreign currency derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
SOUTHERN Co GAS
Derivatives, Fair Value [Line Items]
Derivatives, assets	434	741
Derivatives, liabilities	562	909
Derivative asset, Gross amounts offset	(316)	(508)
Derivative liability, Gross amounts offset	(506)	(785)
Derivative asset	118	233
Derivative liability	56	124
Collateral already posted, aggregate fair value	190	277
Weather derivative premium	11	8
SOUTHERN Co GAS | Gain (loss) on energy-related cash flow hedges
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	2
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges
Derivatives, Fair Value [Line Items]
Derivatives, assets	430	739
Derivatives, liabilities	560	899
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	171	180
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	269	325
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	259	559
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Gain (loss) on energy-related cash flow hedges | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	291	574
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	2
Derivatives, liabilities	1	9
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	0
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	1
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	2
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	8
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	1	1
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Assets from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	1
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Assets held for sale, current
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Derivatives designated as hedging instruments for regulatory purposes | Gain (loss) on energy-related cash flow hedges | Liabilities held for sale, current
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	$ 0	$ 6

Derivatives - Pre-tax Effects o

Derivatives - Pre-tax Effects of Derivatives Designated as Cash Flow Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	$ 190
Gain (Loss) Recognized in OCI on Derivative	(39)	$ 63
SOUTHERN POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(39)	64
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	190		$ 277
Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(9)		(40)
Gain (Loss) Recognized in OCI on Derivative	0	12
Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(5)		(19)
Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(11)		(16)
Energy-related derivatives | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)			(6)
Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	7		1
Energy-related derivatives | ALABAMA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(2)		(6)
Energy-related derivatives | ALABAMA POWER CO | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)		(3)
Energy-related derivatives | ALABAMA POWER CO | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(2)		(3)
Energy-related derivatives | ALABAMA POWER CO | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)			0
Energy-related derivatives | ALABAMA POWER CO | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	1		0
Energy-related derivatives | GEORGIA POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(7)		(15)
Energy-related derivatives | GEORGIA POWER CO | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(2)		(6)
Energy-related derivatives | GEORGIA POWER CO | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(6)		(9)
Energy-related derivatives | GEORGIA POWER CO | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)			0
Energy-related derivatives | GEORGIA POWER CO | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	1		0
Energy-related derivatives | MISSISSIPPI POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(3)		(6)
Energy-related derivatives | MISSISSIPPI POWER CO | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)		(2)
Energy-related derivatives | MISSISSIPPI POWER CO | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(3)		(4)
Energy-related derivatives | MISSISSIPPI POWER CO | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)			0
Energy-related derivatives | MISSISSIPPI POWER CO | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	1		0
Energy-related derivatives | SOUTHERN POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	0	11
Energy-related derivatives | SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	3		(7)
Collateral already posted, aggregate fair value	2
Energy-related derivatives | SOUTHERN Co GAS | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	(1)		(8)
Energy-related derivatives | SOUTHERN Co GAS | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	0		0
Energy-related derivatives | SOUTHERN Co GAS | Assets held for sale, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)			0
Energy-related derivatives | SOUTHERN Co GAS | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Total energy-related derivative gains (losses)	4		$ 1
Interest rate derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	0	(2)
Foreign currency derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	(39)	53
Foreign currency derivatives | SOUTHERN POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative	$ (39)	$ 53

Derivatives - Location and Amou

Derivatives - Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Depreciation and amortization	$ 751	$ 769
Total interest expense, net of amounts capitalized	(430)	(458)
Total other income (expense), net	78	60
Cash Flow Hedging | Gain (loss) on energy-related cash flow hedges | Total depreciation and amortization
Derivative [Line Items]
Gain (loss) on hedge	(3)	1
Cash Flow Hedging | Interest rate derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(5)	(5)
Cash Flow Hedging | Foreign currency derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(5)
Cash Flow Hedging | Foreign currency derivatives | Total other income (expense), net
Derivative [Line Items]
Gain (loss) on hedge	(24)	36
Fair Value Hedging | Interest rate derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	14	(24)
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	119	114
Total interest expense, net of amounts capitalized	(44)	(47)
Total other income (expense), net	2	3
SOUTHERN POWER CO | Cash Flow Hedging | Gain (loss) on energy-related cash flow hedges | Total depreciation and amortization
Derivative [Line Items]
Gain (loss) on hedge	(3)	1
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(5)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Total other income (expense), net
Derivative [Line Items]
Gain (loss) on hedge	(24)	36
SOUTHERN Co GAS
Derivative [Line Items]
Depreciation and amortization	118	129
Total interest expense, net of amounts capitalized	(59)	(59)
Total other income (expense), net	$ 5	$ 12

Derivatives - Cumulative Basis

Derivatives - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (499)	$ (498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	1	2
Securities due within one year | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	(499)	(498)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	1	2
Long-term debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	(2,065)	(2,052)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	28	41
Long-term debt | GEORGIA POWER CO
Derivative [Line Items]
Carrying Amount of the Hedged Item	0	0
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 0	$ 0

Derivatives - Pre-tax Effects_2

Derivatives - Pre-tax Effects of Derivatives Not Designated as Hedging (Details) - Derivatives not designated as hedging instruments - Energy-related derivatives - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 41	$ (13)
Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	33	(15)
Total cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	8	2
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	41	(13)
SOUTHERN Co GAS | Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	33	(15)
SOUTHERN Co GAS | Total cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 8	$ 2

Acquisitions and Dispositions -

Acquisitions and Dispositions - Southern Company's Sale of Gulf Power (Details) - USD ($) $ in Millions	Jan. 01, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Preliminary gain		$ 2,503	$ (1)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses, net of cash divested	$ 5,800
Amount of indebtedness assumed at closing	$ 1,300
Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO | Scenario, Forecast
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Preliminary gain				$ 2,500
Preliminary gain, net of tax				$ 1,300

Acquisitions and Dispositions_2

Acquisitions and Dispositions - Southern Power Narrative (Details) $ in Millions	14 Months Ended
	Dec. 31, 2019USD ($)MW	May 31, 2019MW	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Construction work in progress			$ 7,598	$ 7,254
Property, plant, and equipment, subject to lien			114,096	116,914
SOUTHERN POWER CO
Business Acquisition [Line Items]
Construction work in progress			409	430
Property, plant, and equipment, subject to lien			15,104	$ 14,883
SOUTHERN POWER CO | Lien
Business Acquisition [Line Items]
Property, plant, and equipment, subject to lien			538
SOUTHERN POWER CO | Disposal Group, Held-for-sale, Not Discontinued Operations | Mankato expansion | Scenario, Forecast
Business Acquisition [Line Items]
Proceeds from divestiture of businesses, net of cash divested	$ 650
Approximate nameplate capacity (MW) | MW	385
SOUTHERN POWER CO | Disposal Group, Held-for-sale, Not Discontinued Operations | Nacogdoches Biomass-Fueled Facility | Subsequent Event | Scenario, Forecast
Business Acquisition [Line Items]
Nacogdoches biomass-fueled facility	$ 460
SOUTHERN POWER CO | Wind Generating Facility
Business Acquisition [Line Items]
Equipment marketed for sale			53
SOUTHERN POWER CO | Series of Construction Projects
Business Acquisition [Line Items]
Construction work in progress			347
SOUTHERN POWER CO | Series of Construction Projects | Minimum
Business Acquisition [Line Items]
Estimated future construction payments			575
SOUTHERN POWER CO | Series of Construction Projects | Maximum
Business Acquisition [Line Items]
Estimated future construction payments			$ 640
SOUTHERN POWER CO | Mankato expansion | Scenario, Forecast
Business Acquisition [Line Items]
Approximate nameplate capacity (MW) | MW		385

Acquisitions and Dispositions_3

Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended	3 Months Ended
	May 31, 2019	Jun. 30, 2020	Dec. 31, 2019	Aug. 31, 2018	May 31, 2018
Wild Horse Mountain | Wild Horse Mountain
Business Acquisition [Line Items]
Ownership percentage by parent					100.00%
Wild Horse Mountain | Wild Horse Mountain | Class B Membership Interest
Business Acquisition [Line Items]
Ownership percentage by parent					100.00%
Reading | Reading
Business Acquisition [Line Items]
Ownership percentage by parent				100.00%
Reading | Reading | Class B Membership Interest
Business Acquisition [Line Items]
Ownership percentage by parent				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_4

Acquisitions and Dispositions - Assets Held for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets Held for Sale:
Current assets	$ 55	$ 393
Liabilities Held for Sale:
Current liabilities	38	425
Other non-current liabilities	39	2,836
SOUTHERN POWER CO
Liabilities Held for Sale:
Current liabilities	9	15
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets Held for Sale:
Current assets	55	393
Total property, plant, and equipment	637	4,583
Goodwill and other intangible assets	82	40
Other non-current assets	44	727
Total Assets Held for Sale	818	5,743
Liabilities Held for Sale:
Current liabilities	38	425
Long-term debt		1,286
Accumulated deferred income taxes		618
Other non-current liabilities	39	932
Total Liabilities Held for Sale	77	3,261
Disposal Group, Held-for-sale, Not Discontinued Operations | SOUTHERN POWER CO
Assets Held for Sale:
Current assets	11	8
Total property, plant, and equipment	604	536
Goodwill and other intangible assets	40	40
Other non-current assets	0	0
Total Assets Held for Sale	655	584
Liabilities Held for Sale:
Current liabilities	9	15
Long-term debt		0
Accumulated deferred income taxes		0
Other non-current liabilities	0	0
Total Liabilities Held for Sale	$ 9	$ 15

Acquisitions and Dispositions_5

Acquisitions and Dispositions - Pre-tax Profit (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
GULF POWER CO
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 55
SOUTHERN POWER CO | Florida Plants
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Earnings before income taxes	$ 8

Leases - Major Categories of Le

Leases - Major Categories of Lease Obligations (Details) $ in Millions	Mar. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Lease obligations	$ 2,236
Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	1,094
Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	803
Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	131
Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	55
Other
Lessee, Lease, Description [Line Items]
Lease obligations	153
ALABAMA POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	198
ALABAMA POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	159
ALABAMA POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	3
ALABAMA POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	1
ALABAMA POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	25
ALABAMA POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	10
GEORGIA POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	1,714
GEORGIA POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	1,606
GEORGIA POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	63
GEORGIA POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	3
GEORGIA POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	26
GEORGIA POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	16
MISSISSIPPI POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	8
MISSISSIPPI POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	0
MISSISSIPPI POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	2
MISSISSIPPI POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	0
MISSISSIPPI POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	3
MISSISSIPPI POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	3
SOUTHERN POWER CO
Lessee, Lease, Description [Line Items]
Lease obligations	393
SOUTHERN POWER CO | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN POWER CO | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	393
SOUTHERN POWER CO | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN POWER CO | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN POWER CO | Other
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS
Lessee, Lease, Description [Line Items]
Lease obligations	84
SOUTHERN Co GAS | Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS | Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	83
SOUTHERN Co GAS | Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS | Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	0
SOUTHERN Co GAS | Other
Lessee, Lease, Description [Line Items]
Lease obligations	$ 1

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Remaining terms	13 years 6 months
Total estimate obligations of leases that have not yet commenced	$ 77
Maximum
Lessee, Lease, Description [Line Items]
Lease term, lease not yet commenced	30 years
Real estate | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
Communication towers | Maximum
Lessee, Lease, Description [Line Items]
Lessee, lease term	10 years
Lessee, renewal period	20 years
Fuel cells | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	15 years
GEORGIA POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	10 years 1 month
Lease obligations	$ 1,543
GEORGIA POWER CO | Real estate | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
GEORGIA POWER CO | Electric generating units | Affiliate
Lessee, Lease, Description [Line Items]
Lease obligations	$ 670
GEORGIA POWER CO | Electric generating units | Minimum
Lessee, Lease, Description [Line Items]
Remaining terms	4 years
GEORGIA POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	18 years
GEORGIA POWER CO | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	5 years
SOUTHERN Co GAS
Lessee, Lease, Description [Line Items]
Remaining terms	9 years
Lease obligations	$ 84
SOUTHERN Co GAS | Maximum
Lessee, Lease, Description [Line Items]
Lessor, remaining term	24 years
SOUTHERN Co GAS | Real estate | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	25 years
SOUTHERN POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	33 years 8 months
Lease obligations	$ 393
Total estimate obligations of leases that have not yet commenced	$ 77
SOUTHERN POWER CO | Maximum
Lessee, Lease, Description [Line Items]
Lease term, lease not yet commenced	30 years
SOUTHERN POWER CO | Land | Maximum
Lessee, Lease, Description [Line Items]
Lessee, lease term	48 years
SOUTHERN POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	28 years
ALABAMA POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	3 years 9 months
Lease obligations	$ 194
ALABAMA POWER CO | Electric generating units | Minimum
Lessee, Lease, Description [Line Items]
Remaining terms	4 years
ALABAMA POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Remaining terms	18 years
ALABAMA POWER CO | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	5 years
MISSISSIPPI POWER CO
Lessee, Lease, Description [Line Items]
Remaining terms	6 years 9 months
Lease obligations	$ 8
MISSISSIPPI POWER CO | Electric generating units | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, sales-type lease	20 years
MISSISSIPPI POWER CO | Outdoor lighting | Maximum
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	5 years

Leases - Balance Sheet Amounts

Leases - Balance Sheet Amounts Recorded for Operating and Financing Leases (Details) $ in Millions	Mar. 31, 2019USD ($)
Operating Leases
Operating lease ROU assets, net, including held for sale	$ 1,926
Operating lease ROU assets, net	1,881
Operating lease obligations - current, including held for sale	239
Operating lease obligations - current	226
Operating lease obligations - non current, including held for sale	1,752
Operating lease obligations - non current	1,720
Total operating lease obligations, including held for sale	1,991
Finance Leases
Finance lease ROU assets, net	242
Finance lease obligations - current	38
Finance lease obligations - noncurrent	207
Total finance lease obligations	245
ALABAMA POWER CO
Operating Leases
Operating lease ROU assets, net	160
Operating lease obligations - current	47
Operating lease obligations - non current	147
Total operating lease obligations	194
Finance Leases
Finance lease ROU assets, net	4
Finance lease obligations - current	1
Finance lease obligations - noncurrent	3
Total finance lease obligations	4
GEORGIA POWER CO
Operating Leases
Operating lease ROU assets, net	1,519
Operating lease obligations - current	139
Operating lease obligations - non current	1,404
Total operating lease obligations	1,543
Finance Leases
Finance lease ROU assets, net	145
Finance lease obligations - current	10
Finance lease obligations - noncurrent	161
Total finance lease obligations	171
MISSISSIPPI POWER CO
Operating Leases
Operating lease ROU assets, net	8
Operating lease obligations - current	3
Operating lease obligations - non current	5
Total operating lease obligations	8
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - noncurrent	0
Total finance lease obligations	0
SOUTHERN POWER CO
Operating Leases
Operating lease ROU assets, net	372
Operating lease obligations - current	22
Operating lease obligations - non current	371
Total operating lease obligations	393
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - noncurrent	0
Total finance lease obligations	0
SOUTHERN Co GAS
Operating Leases
Operating lease ROU assets, net	86
Operating lease obligations - current	13
Operating lease obligations - non current	71
Total operating lease obligations	84
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - noncurrent	0
Total finance lease obligations	$ 0

Leases - Lease Costs (Details)

Leases - Lease Costs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Lease cost
Operating lease cost	$ 69
Finance lease cost:
Amortization of ROU assets	7
Interest on lease obligations	3
Total finance lease cost	10
Short-term lease costs	14
Variable lease cost	19
Sublease income	0
Total lease cost	112
ALABAMA POWER CO
Lease cost
Operating lease cost	7
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	5
Variable lease cost	0
Sublease income	0
Total lease cost	12
GEORGIA POWER CO
Lease cost
Operating lease cost	49
Finance lease cost:
Amortization of ROU assets	4
Interest on lease obligations	4
Total finance lease cost	8
Short-term lease costs	3
Variable lease cost	16
Sublease income	0
Total lease cost	76
MISSISSIPPI POWER CO
Lease cost
Operating lease cost	1
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	0
Variable lease cost	0
Sublease income	0
Total lease cost	1
SOUTHERN POWER CO
Lease cost
Operating lease cost	7
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	0
Variable lease cost	1
Sublease income	0
Total lease cost	8
SOUTHERN Co GAS
Lease cost
Operating lease cost	4
Finance lease cost:
Amortization of ROU assets	0
Interest on lease obligations	0
Total finance lease cost	0
Short-term lease costs	0
Variable lease cost	0
Sublease income	0
Total lease cost	$ 4

Leases - Other Information (Det

Leases - Other Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 74
Operating cash flows from finance leases	6
Financing cash flows from finance leases	8
ROU assets obtained in exchange for new operating lease obligations	15
ROU assets obtained in exchange for new finance lease obligations	$ 29
Weighted-average remaining lease term in years:
Operating leases	13 years 6 months
Finance leases	18 years 6 months
Weighted-average discount rate:
Operating leases	4.49%
Finance leases	5.00%
ALABAMA POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 13
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	2
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	3 years 9 months
Finance leases	14 years 9 months
Weighted-average discount rate:
Operating leases	3.33%
Finance leases	3.75%
GEORGIA POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 32
Operating cash flows from finance leases	13
Financing cash flows from finance leases	2
ROU assets obtained in exchange for new operating lease obligations	4
ROU assets obtained in exchange for new finance lease obligations	$ 28
Weighted-average remaining lease term in years:
Operating leases	10 years 1 month
Finance leases	11 years 3 months
Weighted-average discount rate:
Operating leases	4.42%
Finance leases	10.68%
MISSISSIPPI POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 1
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	0
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	6 years 9 months
Weighted-average discount rate:
Operating leases	4.03%
SOUTHERN POWER CO
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 7
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	0
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	33 years 8 months
Weighted-average discount rate:
Operating leases	5.68%
SOUTHERN Co GAS
Cash paid for amounts included in the measurements of lease obligations:
Operating cash flows from operating leases	$ 4
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for new operating lease obligations	0
ROU assets obtained in exchange for new finance lease obligations	$ 0
Weighted-average remaining lease term in years:
Operating leases	9 years
Weighted-average discount rate:
Operating leases	3.70%

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019USD ($)
Operating leases:
2019 (remaining)	$ 253
2020	291
2021	274
2022	263
2023	198
Thereafter	1,637
Total	2,916
Less: Present value discount	925
Operating lease obligations, including held for sale	1,991
Finance leases:
2019 (remaining)	24
2020	32
2021	26
2022	22
2023	18
Thereafter	273
Total	395
Less: Present value discount	150
Finance lease obligations	245
ALABAMA POWER CO
Operating leases:
2019 (remaining)	46
2020	53
2021	52
2022	52
2023	3
Thereafter	1
Total	207
Less: Present value discount	13
Operating lease obligations	194
Finance leases:
2019 (remaining)	1
2020	1
2021	1
2022	1
2023	1
Thereafter	0
Total	5
Less: Present value discount	1
Finance lease obligations	4
GEORGIA POWER CO
Operating leases:
2019 (remaining)	182
2020	202
2021	197
2022	195
2023	196
Thereafter	984
Total	1,956
Less: Present value discount	413
Operating lease obligations	1,543
Finance leases:
2019 (remaining)	22
2020	28
2021	25
2022	25
2023	25
Thereafter	165
Total	290
Less: Present value discount	119
Finance lease obligations	171
MISSISSIPPI POWER CO
Operating leases:
2019 (remaining)	2
2020	2
2021	1
2022	1
2023	1
Thereafter	2
Total	9
Less: Present value discount	1
Operating lease obligations	8
Finance leases:
2019 (remaining)	0
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	0
SOUTHERN POWER CO
Operating leases:
2019 (remaining)	17
2020	22
2021	23
2022	23
2023	24
Thereafter	848
Total	957
Less: Present value discount	564
Operating lease obligations	393
Finance leases:
2019 (remaining)	0
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	0
SOUTHERN Co GAS
Operating leases:
2019 (remaining)	12
2020	16
2021	16
2022	12
2023	10
Thereafter	36
Total	102
Less: Present value discount	18
Operating lease obligations	84
Finance leases:
2019 (remaining)	0
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	$ 0

Leases - Lease Income (Details)

Leases - Lease Income (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	$ 2
Lease income - operating leases	71
Variable lease income	66
Total lease income	139
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	19
Variable lease income	0
Total lease income	19
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	2
Lease income - operating leases	0
Variable lease income	0
Total lease income	2
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	41
Variable lease income	72
Total lease income	113
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
Lease income - interest income on sales-type leases	0
Lease income - operating leases	9
Variable lease income	0
Total lease income	$ 9

Leases - Undiscounted Cash Flow

Leases - Undiscounted Cash Flows to be Received Under Tolling Arrangements Accounted for as Sales-type Leases (Details) $ in Millions	Mar. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
2019 (remaining)	$ 11
2020	14
2021	14
2022	13
2023	12
Thereafter	135
Total undiscounted cash flows	199
Lease receivable	108
Difference between undiscounted cash flows and discounted cash flows	91
MISSISSIPPI POWER CO
Lessor, Lease, Description [Line Items]
2019 (remaining)	11
2020	14
2021	14
2022	13
2023	12
Thereafter	135
Total undiscounted cash flows	199
Lease receivable	108
Difference between undiscounted cash flows and discounted cash flows	$ 91

Leases - Undiscounted Cash Fl_2

Leases - Undiscounted Cash Flows to be Received Under PPAs Accounted for as Operating Leases (Details) $ in Millions	Mar. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
2019 (remaining)	$ 163
2020	188
2021	183
2022	174
2023	171
Thereafter	1,809
Total	2,688
GEORGIA POWER CO
Lessor, Lease, Description [Line Items]
2019 (remaining)	20
2020	26
2021	18
2022	8
2023	2
Thereafter	0
Total	74
SOUTHERN POWER CO
Lessor, Lease, Description [Line Items]
2019 (remaining)	123
2020	128
2021	131
2022	134
2023	137
Thereafter	1,017
Total	1,670
SOUTHERN Co GAS
Lessor, Lease, Description [Line Items]
2019 (remaining)	26
2020	34
2021	34
2022	34
2023	34
Thereafter	498
Total	$ 660

Segment and Related Informati_3

Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)statepipelinesegment	Mar. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	3
Total operating revenues	$ 5,412	$ 6,372
Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	1,474	1,607
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Total operating revenues	443	509
SOUTHERN POWER CO | Wholesale revenues, affiliates
Segment Reporting Information [Line Items]
Total operating revenues	87	83
SOUTHERN POWER CO | Traditional Electric Operating Companies | Wholesale revenues, affiliates
Segment Reporting Information [Line Items]
Total operating revenues	$ 87	83
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	4
Total operating revenues	$ 1,474	1,639
Number of reportable segments | segment	4
SOUTHERN Co GAS | Pipeline
Segment Reporting Information [Line Items]
Number of pipeline construction projects | pipeline	2
SOUTHERN Co GAS | SNG
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
SOUTHERN Co GAS | Dalton Pipeline
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
SOUTHERN Co GAS | Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	$ 1,476	1,631
SOUTHERN Co GAS | Traditional Electric Operating Companies | Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	0	0
SOUTHERN Co GAS | Southern Company | Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	$ 17	$ 36

Segment and Related Informati_4

Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)utility	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Operating revenues	$ 5,412	$ 6,372
Segment net income (loss)	2,084	938
Goodwill	5,284		$ 5,315
Total assets	114,096		116,914
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,474	1,639
Segment net income (loss)	270	279
Goodwill	5,015		5,015
Total assets	20,952		21,448
Goodwill impairment	0	$ 42
SOUTHERN Co GAS | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting Information [Line Items]
Number of natural gas distribution utilities disposed | utility		3
Traditional Electric Operating Companies | GEORGIA POWER AND MISSISSIPPI POWER CO | Kemper County Energy Facility
Segment Reporting Information [Line Items]
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment	2	$ 44
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment after tax	1	33
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,474	1,639
SOUTHERN Co GAS | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Pivotal Home Solutions
Segment Reporting Information [Line Items]
Goodwill impairment		42
All Other | Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO
Segment Reporting Information [Line Items]
Preliminary pre-tax gain	2,500
Preliminary after-tax gain	1,300
Gas Distribution Operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	4,034
Gas Distribution Operations | SOUTHERN Co GAS | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting Information [Line Items]
Operating revenues		167
Gas Marketing Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	981
Operating revenues		32
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,495	1,657
Segment net income (loss)	273	293
Total assets	21,592		21,918
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,474	1,639
Segment net income (loss)	270	279
Goodwill	5,015		5,015
Total assets	20,952		21,448
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	182	401
Segment net income (loss)	1,195	(74)
Goodwill	268		298
Total assets	3,391		3,285
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	11	15
Segment net income (loss)	(3)	(14)
Total assets	10,900		11,112
Operating Segments | Gas Distribution Operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,172	1,212
Segment net income (loss)	133	149
Total assets	17,379		17,266
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	8	8
Segment net income (loss)	32	27
Total assets	1,781		1,763
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	86	166
Segment net income (loss)	47	104
Total assets	821		1,302
Less Gross Gas Costs	1,928	1,939
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS | Third Party Gross Revenues
Segment Reporting Information [Line Items]
Operating revenues	1,926	1,938
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS | Intercompany Revenues
Segment Reporting Information [Line Items]
Operating revenues	88	167
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS | Total Gross Revenues
Segment Reporting Information [Line Items]
Operating revenues	2,014	2,105
Operating Segments | Gas Marketing Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	229	271
Segment net income (loss)	61	13
Total assets	1,611		1,587
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(39)	(50)
Segment net income (loss)	(2)	0
Goodwill	(1)		0
Total assets	(1,370)		(1,778)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(32)	(33)
Segment net income (loss)	0	0
Total assets	(11,540)		(11,582)
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	3,795	4,382
Segment net income (loss)	621	733
Goodwill	2		2
Total assets	91,123		93,959
Electric Utilities | Operating Segments | Traditional Electric Operating Companies
Segment Reporting Information [Line Items]
Operating revenues	3,445	3,979
Segment net income (loss)	565	612
Goodwill	0		0
Total assets	76,798		79,382
Electric Utilities | Operating Segments | SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	443	509
Segment net income (loss)	56	121
Goodwill	2		2
Total assets	15,104		14,883
Electric Utilities | Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(93)	(106)
Segment net income (loss)	0	$ 0
Goodwill	0		0
Total assets	$ (779)		$ (306)

Segment and Related Informati_5

Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Concentration Risk [Line Items]
Operating revenues	$ 5,412	$ 6,372
Retail
Concentration Risk [Line Items]
Operating revenues	3,084	3,568
Wholesale
Concentration Risk [Line Items]
Operating revenues	499	623
Other
Concentration Risk [Line Items]
Operating revenues	168	161
Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues	1,163	1,224
Electric Utilities' Revenues
Concentration Risk [Line Items]
Operating revenues	3,795	4,382
Electric Utilities' Revenues | Retail
Concentration Risk [Line Items]
Operating revenues	3,084	3,568
Electric Utilities' Revenues | Wholesale
Concentration Risk [Line Items]
Operating revenues	499	623
Electric Utilities' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	212	191
Southern Company Gas' Revenues
Concentration Risk [Line Items]
Operating revenues	1,474	1,639
Southern Company Gas' Revenues | Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues	1,161	1,200
Southern Company Gas' Revenues | Gas Distribution Operations | Revenues | Product Concentration Risk | Three Gas Distribution Operations
Concentration Risk [Line Items]
Operating revenues		167
Southern Company Gas' Revenues | Gas Marketing Services
Concentration Risk [Line Items]
Operating revenues	229	271
Southern Company Gas' Revenues | Gas Marketing Services | Revenues | Product Concentration Risk | Pivotal Home Solutions
Concentration Risk [Line Items]
Operating revenues		32
Southern Company Gas' Revenues | Other
Concentration Risk [Line Items]
Operating revenues	$ 84	$ 168