Joint Ownership Agreements (Tables)

12 Months Ended

Dec. 31, 2016

Jointly Owned Utility Plant Interests [Line Items]

Schedule of percentage ownership and investment in jointly-owned facilities

At December 31, 2016, Alabama Power's, Georgia Power's, and Southern Power's percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation with the above entities were as follows:

Facility (Type)	Percent Ownership		Plant in Service		Accumulated Depreciation		CWIP
			(in millions)
Plant Vogtle (nuclear) Units 1 and 2	45.7	%	$	3,545	$	2,111	$	74
Plant Hatch (nuclear)	50.1		1,297		585		81
Plant Miller (coal) Units 1 and 2	91.8		1,657		587		23
Plant Scherer (coal) Units 1 and 2	8.4		258		90		3
Plant Wansley (coal)	53.5		1,046		308		12
Rocky Mountain (pumped storage)	25.4		181		129		—
Plant Stanton (combined cycle) Unit A	65.0		155		58		—

Temporary Equity

The following table presents changes during the year in redeemable preferred stock of subsidiaries for Southern Company:

	Redeemable Preferred Stock of Subsidiaries
	(in millions)
Balance at December 31, 2013	$	375
Issued	—
Redeemed	—
Balance at December 31, 2014	375
Issued	—
Redeemed	(262		)
Other	5
Balance at December 31, 2015	118
Issued	—
Redeemed	—
Balance at December 31, 2016	$	118

Alabama Power [Member]

Jointly Owned Utility Plant Interests [Line Items]

Schedule of percentage ownership and investment in jointly-owned facilities

In addition to the Company's ownership of SEGCO and joint ownership of an associated gas pipeline, the Company's percentage ownership and investment in jointly-owned generating plants at December 31, 2016 were as follows:

Facility	Total MW Capacity	Company Ownership			Plant in Service		Accumulated Depreciation		Construction Work in Progress
					(in millions)
Greene County	500	60.00	%	(1)	$	168	$	66	$	1
Plant Miller
Units 1 and 2	1,320	91.84	%	(2)	1,657		587		23

(1) Jointly owned with an affiliate, Mississippi Power.

(2) Jointly owned with PowerSouth Energy Cooperative, Inc.

Georgia Power [Member]

Jointly Owned Utility Plant Interests [Line Items]

Schedule of percentage ownership and investment in jointly-owned facilities

At December 31, 2016, the Company's percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation with the above entities were as follows:

Facility (Type)	Company Ownership		Plant in Service		Accumulated Depreciation		CWIP
			(in millions)
Plant Vogtle (nuclear)
Units 1 and 2	45.7	%	$	3,545	$	2,111	$	74
Plant Hatch (nuclear)	50.1		1,297		585		81
Plant Wansley (coal)	53.5		1,046		308		12
Plant Scherer (coal)
Units 1 and 2	8.4		258		90		3
Unit 3	75.0		1,203		458		23
Rocky Mountain (pumped storage)	25.4		181		129		—

Gulf Power [Member]

Jointly Owned Utility Plant Interests [Line Items]

Schedule of percentage ownership and investment in jointly-owned facilities

At December 31, 2016, the Company's percentage ownership and investment in these jointly-owned facilities were as follows:

	Plant Scherer Unit 3 (coal)			Plant Daniel Units 1 & 2 (coal)
	(in millions)
Plant in service	$	398		$	680
Accumulated depreciation	143			202
Construction work in progress	7			7
Company ownership	25		%	50		%

Mississippi Power [Member]

Jointly Owned Utility Plant Interests [Line Items]

Schedule of percentage ownership and investment in jointly-owned facilities

At December 31, 2016, the Company's percentage ownership and investment in these jointly-owned facilities in commercial operation were as follows:

Generating Plant	Company Ownership		Plant in Service		Accumulated Depreciation		CWIP
			(in millions)
Greene County
Units 1 and 2	40	%	$	165	$	48	$	—
Daniel
Units 1 and 2	50	%	$	695	$	173	$	15

Southern Company Gas [Member]

Jointly Owned Utility Plant Interests [Line Items]

Temporary Equity

The roll-forwards of the redeemable noncontrolling interest for the successor period of July 1, 2016 through December 31, 2016 and the predecessor period of January 1, 2016 through June 30, 2016 are detailed below:

Predecessor –	(in millions)
Balance at December 31, 2015	$	—
Reclassification of noncontrolling interest to contingently redeemable noncontrolling interest	46
Net income attributable to noncontrolling interest	14
Distribution to noncontrolling interest	(19		)
Balance at June 30, 2016	$	41
Successor –	(in millions)
Balance at July 1, 2016	$	174
Reclassification of contingently redeemable noncontrolling interest to mandatorily redeemable noncontrolling interest	(174		)
Balance at December 31, 2016	$	—

Equity Method Investments

The carrying amounts of the Company's equity method investments as of December 31, 2016 and 2015 and related income from those investments for the successor period ended December 31, 2016 and predecessor periods ended June 30, 2016 and December 31, 2015 and 2014 were as follows:

Balance Sheet Information	Successor		Predecessor
	December 31, 2016		December 31, 2015
	(in millions)		(in millions)
SNG	$	1,394	$	—
Triton	44		49
Horizon Pipeline	30		14
PennEast Pipeline	22		9
Atlantic Coast Pipeline	33		7
Pivotal JAX LNG, LLC	16		—
Other	2		1
Total	$	1,541	$	80

Income Statement Information	Successor		Predecessor
	July 1, 2016 through December 31, 2016		January 1, 2016 through June 30, 2016		2015		2014
	(in millions)		(in millions)
SNG	$	56	$	—	$	—	$	—
Triton	2		1		4		6
Horizon Pipeline	1		1		2		2
Atlantic Coast Pipeline	1		—		—		—
Total	$	60	$	2	$	6	$	8

Selected financial information of SNG since the Company's September 1, 2016 acquisition of a 50% equity interest is as follows:

Balance Sheet Information	As of December 31, 2016
	(in millions)
Current assets	$	95
Property, plant, and equipment	2,451
Deferred charges and other assets	129
Total Assets	$	2,675
Current liabilities	$	588
Long-term debt	706
Other deferred charges and other liabilities	22
Total Liabilities	$	1,316
Total Stockholders' Equity	1,359
Total Liabilities and Stockholders' Equity	$	2,675

Income Statement Information	September 1, 2016 through December 31, 2016
	(in millions)
Revenues	$	230
Operating income	$	138
Net income	$	115