Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Assets and liabilities measured at fair value on a recurring basis

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Financial instruments not having carrying amount equal to fair value

At December 31, 2018 and 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:

	Southern   Company(a)(b)		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas(b)
	(in millions)
At December 31, 2018:
Long-term debt, including securities due within one year:
Carrying amount	$	45,023	$	8,120	$	9,838	$	1,579	$	5,017	$	5,940
Fair value	44,824		8,370		9,800		1,546		4,980		5,965
At December 31, 2017:
Long-term debt, including securities due within one year:
Carrying amount	$	48,151	$	7,625	$	11,777	$	2,086	$	5,841	$	6,048
Fair value	51,348		8,305		12,531		2,076		6,079		6,471

(a) Includes long-term debt of Gulf Power, which is classified as liabilities held for sale on Southern Company's balance sheet at December 31, 2018. See Note 15 under "Southern Company's Sale of Gulf Power" and "Assets Held for Sale" for additional information.

(b) The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the Merger. Southern Company Gas amortizes the fair value adjustments over the lives of the respective bonds.