Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

Details of AROs included in the balance sheets

Details of the AROs included in the balance sheets are as follows:

	Southern Company			Alabama Power			Georgia Power			Mississippi Power			Southern Power
	(in millions)
Balance at December 31, 2016	$	4,514		$	1,533		$	2,532		$	179		$	64
Liabilities incurred	16			—			4			—			6
Liabilities settled	(177		)	(26		)	(120		)	(23		)	—
Accretion	179			77			89			5			4
Cash flow revisions	292			125			133			13			4
Balance at December 31, 2017	$	4,824		$	1,709		$	2,638		$	174		$	78
Liabilities incurred	29			—			27			—			2
Liabilities settled	(244		)	(55		)	(116		)	(35		)	—
Accretion	217			106			94			5			4
Cash flow revisions	4,737			1,450			3,186			16			—
Reclassification to held for sale	(169		)	—			—			—			—
Balance at December 31, 2018	$	9,394		$	3,210		$	5,829		$	160		$	84

Investment securities in the Funds

Investment securities in the Funds for December 31, 2018 and 2017 were as follows:

	Southern Company		Alabama Power		Georgia Power
	(in millions)
At December 31, 2018:
Equity securities	$	919	$	594	$	325
Debt securities	726		201		525
Other securities	74		51		23
Total investment securities in the Funds	$	1,719	$	846	$	873
At December 31, 2017:
Equity securities	$	1,059	$	644	$	415
Debt securities	725		223		502
Other securities	47		35		12
Total investment securities in the Funds	$	1,831	$	902	$	929

Fair value increases (decreases) of the Funds

The fair value increases (decreases) of the Funds, including reinvested interest and dividends and excluding the Funds' expenses, for 2018, 2017, and 2016 are shown in the table below. The fair value increases (decreases) included unrealized gains (losses) on securities held in the Funds at each of December 31, 2018, 2017, and 2016, which are also shown in the table below.

	Southern Company			Alabama Power			Georgia Power
	(in millions)
Fair value increases (decreases)
2018	$	(67	)	$	(38	)	$	(29	)
2017	233			125			108
2016	114			76			38
Unrealized gains (losses)
At December 31, 2018	$	(183	)	$	(96	)	$	(87	)
At December 31, 2017	181			98			83
At December 31, 2016	48			34			14

At December 31, 2018, assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows:

	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs		Net Asset Value as a Practical Expedient
At December 31, 2018:	(Level 1)		(Level 2)		(Level 3)		(NAV)		Total
	(in millions)
Southern Company
Assets:
Energy-related derivatives(a)(b)	$	469	$	292	$	—	$	—	$	761
Foreign currency derivatives	—		75		—		—		75
Investments in trusts:(c)(d)
Domestic equity	601		107		—		—		708
Foreign equity	53		173		—		—		226
U.S. Treasury and government agency securities	—		261		—		—		261
Municipal bonds	—		83		—		—		83
Pooled funds – fixed income	—		14		—		—		14
Corporate bonds	24		290		—		—		314
Mortgage and asset backed securities	—		68		—		—		68
Private equity	—		—		—		45		45
Cash and cash equivalents	16		—		—		—		16
Other	34		4		—		—		38
Cash equivalents	765		1		—		—		766
Other investments	—		12		—		—		12
Total	$	1,962	$	1,380	$	—	$	45	$	3,387
Liabilities:
Energy-related derivatives(a)(b)	$	648	$	316	$	—	$	—	$	964
Interest rate derivatives	—		49		—		—		49
Foreign currency derivatives	—		23		—		—		23
Contingent consideration	—		—		21		—		21
Total	$	648	$	388	$	21	$	—	$	1,057

	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs		Net Asset Value as a Practical Expedient
At December 31, 2018:	(Level 1)		(Level 2)		(Level 3)		(NAV)		Total
	(in millions)
Alabama Power
Assets:
Energy-related derivatives	$	—	$	6	$	—	$	—	$	6
Nuclear decommissioning trusts:(c)
Domestic equity	396		95		—		—		491
Foreign equity	53		50		—		—		103
U.S. Treasury and government agency securities	—		18		—		—		18
Municipal bonds	—		1		—		—		1
Corporate bonds	24		135		—		—		159
Mortgage and asset backed securities	—		23		—		—		23
Private equity	—		—		—		45		45
Other	6		—		—		—		6
Cash equivalents	116		1		—		—		117
Other investments	—		12		—		—		12
Total	$	595	$	341	$	—	$	45	$	981
Liabilities:
Energy-related derivatives	$	—	$	10	$	—	$	—	$	10
Georgia Power
Assets:
Energy-related derivatives	$	—	$	6	$	—	$	—	$	6
Nuclear decommissioning trusts:(c)(d)
Domestic equity	205		1		—		—		206
Foreign equity	—		119		—		—		119
U.S. Treasury and government agency securities	—		243		—		—		243
Municipal bonds	—		82		—		—		82
Corporate bonds	—		155		—		—		155
Mortgage and asset backed securities	—		45		—		—		45
Other	19		4		—		—		23
Total	$	224	$	655	$	—	$	—	$	879
Liabilities:
Energy-related derivatives	$	—	$	21	$	—	$	—	$	21
Interest rate derivatives	—		2		—		—		2
Total	$	—	$	23	$	—	$	—	$	23

	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs		Net Asset Value as a Practical Expedient
At December 31, 2018:	(Level 1)		(Level 2)		(Level 3)		(NAV)		Total
	(in millions)
Mississippi Power
Assets:
Energy-related derivatives	$	—	$	3	$	—	$	—	$	3
Cash equivalents	255		—		—		—		255
Total	$	255	$	3	$	—	$	—	$	258
Liabilities:
Energy-related derivatives	$	—	$	9	$	—	$	—	$	9
Southern Power
Assets:
Energy-related derivatives	$	—	$	4	$	—	$	—	$	4
Foreign currency derivatives	—		75		—		—		75
Cash equivalents	46		—		—		—		46
Total	$	46	$	79	$	—	$	—	$	125
Liabilities:
Energy-related derivatives	$	—	$	8	$	—	$	—	$	8
Foreign currency derivatives	—		23		—		—		23
Contingent consideration	—		—		21		—		21
Total	$	—	$	31	$	21	$	—	$	52
Southern Company Gas
Assets:
Energy-related derivatives(a)(b)	$	469	$	272	$	—	$	—	$	741
Non-qualified deferred compensation trusts:
Domestic equity	—		11		—		—		11
Foreign equity	—		4		—		—		4
Pooled funds - fixed income	—		14		—		—		14
Cash equivalents	4		—		—		—		4
Cash equivalents	40		—		—		—		40
Total	$	513	$	301	$	—	$	—	$	814
Liabilities:
Energy-related derivatives(a)(b)	$	648	$	261	$	—	$	—	$	909

(a) Energy-related derivatives exclude $8 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value.

(b) Energy-related derivatives exclude cash collateral of $277 million.

(c) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information.

(d) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information.

At December 31, 2017, assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows:

	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs		Net Asset Value as a Practical Expedient
At December 31, 2017:	(Level 1)		(Level 2)		(Level 3)		(NAV)		Total
	(in millions)
Southern Company
Assets:
Energy-related derivatives(a)(b)	$	331	$	239	$	—	$	—	$	570
Interest rate derivatives	—		1		—		—		1
Foreign currency derivatives	—		129		—		—		129
Nuclear decommissioning trusts:(c)
Domestic equity	690		82		—		—		772
Foreign equity	62		224		—		—		286
U.S. Treasury and government agency securities	—		251		—		—		251
Municipal bonds	—		68		—		—		68
Corporate bonds	21		315		—		—		336
Mortgage and asset backed securities	—		57		—		—		57
Private equity	—		—		—		29		29
Other	19		12		—		—		31
Cash equivalents	1,455		—		—		—		1,455
Other investments	9		—		1		—		10
Total	$	2,587	$	1,378	$	1	$	29	$	3,995
Liabilities:
Energy-related derivatives(a)(b)	$	480	$	253	$	—	$	—	$	733
Interest rate derivatives	—		38		—		—		38
Foreign currency derivatives	—		23		—		—		23
Contingent consideration	—		—		22		—		22
Total	$	480	$	314	$	22	$	—	$	816

	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs		Net Asset Value as a Practical Expedient
At December 31, 2017:	(Level 1)		(Level 2)		(Level 3)		(NAV)		Total
	(in millions)
Alabama Power
Assets:
Energy-related derivatives	$	—	$	4	$	—	$	—	$	4
Nuclear decommissioning trusts:(d)
Domestic equity	442		81		—		—		523
Foreign equity	62		59		—		—		121
U.S. Treasury and government agency securities	—		24		—		—		24
Corporate bonds	21		160		—		—		181
Mortgage and asset backed securities	—		18		—		—		18
Private equity	—		—		—		29		29
Other	6		—		—		—		6
Cash equivalents	349		—		—		—		349
Total	$	880	$	346	$	—	$	29	$	1,255
Liabilities:
Energy-related derivatives	$	—	$	10	$	—	$	—	$	10
Georgia Power
Assets:
Energy-related derivatives	$	—	$	6	$	—	$	—	$	6
Nuclear decommissioning trusts:(d)(e)
Domestic equity	248		1		—		—		249
Foreign equity	—		166		—		—		166
U.S. Treasury and government agency securities	—		227		—		—		227
Municipal bonds	—		68		—		—		68
Corporate bonds	—		155		—		—		155
Mortgage and asset backed securities	—		40		—		—		40
Other	12		12		—		—		24
Cash equivalents	690		—		—		—		690
Total	$	950	$	675	$	—	$	—	$	1,625
Liabilities:
Energy-related derivatives	$	—	$	19	$	—	$	—	$	19
Interest rate derivatives	—		5		—		—		5
Total	$	—	$	24	$	—	$	—	$	24

	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs		Net Asset Value as a Practical Expedient
At December 31, 2017:	(Level 1)		(Level 2)		(Level 3)		(NAV)		Total
	(in millions)
Mississippi Power
Assets:
Energy-related derivatives	$	—	$	2	$	—	$	—	$	2
Interest rate derivatives	—		1		—		—		1
Cash equivalents	224		—		—		—		224
Total	$	224	$	3	$	—	$	—	$	227
Liabilities:
Energy-related derivatives	$	—	$	9	$	—	$	—	$	9
Southern Power
Assets:
Energy-related derivatives	$	—	$	3	$	—	$	—	$	3
Foreign currency derivatives	—		129		—		—		129
Cash equivalents	21		—		—		—		21
Total	$	21	$	132	$	—	$	—	$	153
Liabilities:
Energy-related derivatives	$	—	$	13	$	—	$	—	$	13
Foreign currency derivatives	—		23		—		—		23
Contingent consideration	—		—		22		—		22
Total	$	—	$	36	$	22	$	—	$	58
Southern Company Gas
Assets:
Energy-related derivatives(a)(b)	$	331	$	223	$	—	$	—	$	554
Liabilities:
Energy-related derivatives(a)(b)	$	479	$	181	$	—	$	—	660

(a) Energy-related derivatives exclude $11 million associated with premiums and certain weather derivatives accounted for based on intrinsic value rather than fair value.

(b) Energy-related derivatives exclude cash collateral of $193 million.

(c) For additional detail, see the nuclear decommissioning trusts sections for Alabama Power and Georgia Power in this table.

(d) Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 under "Nuclear Decommissioning" for additional information.

(e) Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. See Note 6 under "Nuclear Decommissioning" for additional information.

Accumulated provisions for the external decommissioning trust funds

At December 31, 2018 and 2017, the accumulated provisions for the external decommissioning trust funds were as follows:

	2018		2017
	(in millions)
Alabama Power
Plant Farley	$	846	$	902
Georgia Power
Plant Hatch	$	547	$	583
Plant Vogtle Units 1 and 2	326		346
Total	$	873	$	929

Estimated costs of decommissioning

The estimated costs of decommissioning at December 31, 2018 based on the most current studies, which were each performed in 2018, were as follows:

	Plant Farley		Plant   Hatch(*)		Plant Vogtle  Units 1 and 2(*)
Decommissioning periods:
Beginning year	2037		2034		2047
Completion year	2076		2075		2079
	(in millions)
Site study costs:
Radiated structures	$	1,234	$	734	$	601
Spent fuel management	387		172		162
Non-radiated structures	99		56		79
Total site study costs	$	1,720	$	962	$	842

(*) Based on Georgia Power's ownership interests.