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jointly owned affiliate equity

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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Joint Ownership Agreements - Narrative (Details) gal in Thousands	6 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) mi MW	Jun. 30, 2016 USD ($)	Oct. 03, 2016 USD ($)	Dec. 31, 2016 USD ($) mi MW gal	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) mi Bcf	Dec. 31, 2008	Oct. 02, 2016	Sep. 01, 2016	Aug. 31, 2016	Feb. 12, 2016 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress	$ 8,977,000,000			$ 8,977,000,000	$ 9,082,000,000
Short-term debt	2,241,000,000			2,241,000,000	1,376,000,000
Earnings from equity method investments			$ 15,000,000	59,000,000	0	$ 0
Distributions to noncontrolling interests				72,000,000	18,000,000	1,000,000
Southern Power [Member]
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress	$ 398,000,000			$ 398,000,000	1,137,000,000
Total megawatt capacity \| MW	659			659
Short-term debt	$ 209,000,000			$ 209,000,000	137,000,000
Distributions to noncontrolling interests				$ 57,000,000	18,000,000	1,000,000
Southern Power [Member] \| Plant Stanton Combined Cycle Unit [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	65.00%			65.00%
Plant in service	$ 155,000,000			$ 155,000,000
Accumulated depreciation	58,000,000			58,000,000
Gulf Power [Member]
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress	51,000,000			51,000,000	48,000,000
Short-term debt	$ 268,000,000			$ 268,000,000	142,000,000
Gulf Power [Member] \| Plant Daniel Units 1 and 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity \| MW	1,000			1,000
Percent ownership	50.00%			50.00%
Plant in service	$ 680,000,000			$ 680,000,000
Accumulated depreciation	$ 202,000,000			$ 202,000,000
Gulf Power [Member] \| Plant Scherer Unit Three [Member]
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity \| MW	818			818
Percent ownership	25.00%			25.00%
Plant in service	$ 398,000,000			$ 398,000,000
Accumulated depreciation	143,000,000			143,000,000
Georgia Power [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage of proportionate share owed in consortium agreement							45.70%
Construction work in progress	4,939,000,000			4,939,000,000	4,775,000,000
Short-term debt	$ 391,000,000			$ 391,000,000	158,000,000
Georgia Power [Member] \| Alabama Power [Member]
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity \| MW	1,020			1,020
Georgia Power [Member] \| Intercession City Combustion Turbine [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership										33.00%
Georgia Power [Member] \| Vogtle Units Three and Four [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	45.70%			45.70%
Georgia Power [Member] \| Plant Scherer Unit Three [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	75.00%			75.00%
Plant in service	$ 1,203,000,000			$ 1,203,000,000
Accumulated depreciation	458,000,000			458,000,000
Georgia Power [Member] \| Southern Electric Generating Company [Member]
Jointly Owned Utility Plant Interests [Line Items]
Share Of purchased power				57,000,000	78,000,000
Alabama Power [Member]
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress	$ 491,000,000			$ 491,000,000	801,000,000
Total megawatt capacity \| MW	1,000			1,000
Jointly owned affiliate equity				$ 108,000,000
Jointly owned affiliate long term debt				125,000,000
Jointly owned affiliate long term debt annual interest requirement				3,000,000
Short-term debt	$ 0			$ 0	0
Ownership percentage, equity method investment	50.00%			50.00%
Percent ownership	14.00%			14.00%
Alabama Power [Member] \| SEGCO [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	86.00%			86.00%
Alabama Power [Member] \| Southern Electric Generating Company [Member]
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity \| MW	1,020			1,020
Share Of purchased power				$ 55,000,000	76,000,000	84,000,000
Unconditional guarantee to pay outstanding pollution control revenue bond principal	$ 25,000,000			25,000,000
Alabama Power [Member] \| SEGCO [Member]
Jointly Owned Utility Plant Interests [Line Items]
Short-term debt	$ 38,000,000			38,000,000
Dividends paid by equity method investment				$ 24,000,000
Southern Company Gas [Member] \| Dalton Pipeline [Member]
Jointly Owned Utility Plant Interests [Line Items]
Costs included in CWIP					$ 33,000,000
Undivided ownership interest to be leased				50.00%	50.00%
Pipeline infrastructure \| mi	115			115
Southern Company Gas [Member] \| Dalton Pipeline Arrangement 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Undivided ownership interest to be leased				50.00%
Future minimum payments receivable	$ 26,000,000			$ 26,000,000
Term of contract				25 years
Maturity December First Two Thousand Eighteen [Member] \| Alabama Power [Member] \| Southern Electric Generating Company [Member]
Jointly Owned Utility Plant Interests [Line Items]
Guarantee of unsecured senior notes	100,000,000			$ 100,000,000
Plant Vogtle Units 3 And 4 [Member] \| Georgia Power [Member]
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress	$ 3,900,000,000			$ 3,900,000,000
Dalton Pipeline Arrangement 1 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percentage of voting interests acquired	50.00%			50.00%
Successor [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress	$ 496,000,000			$ 496,000,000
Short-term debt	1,257,000,000			1,257,000,000
Earnings from equity method investments	60,000,000
Distributions to noncontrolling interests	15,000,000
Successor [Member] \| Southern Company Gas [Member] \| Dalton Pipeline [Member]
Jointly Owned Utility Plant Interests [Line Items]
Costs included in CWIP	$ 124,000,000			$ 124,000,000
Predecessor [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Construction work in progress					$ 414,000,000
Short-term debt					1,010,000,000
Earnings from equity method investments		$ 2,000,000			6,000,000	8,000,000
Distributions to noncontrolling interests		19,000,000			$ 18,000,000	17,000,000
Purchased Power from Affiliates [Member] \| Georgia Power [Member] \| Southern Electric Generating Company [Member]
Jointly Owned Utility Plant Interests [Line Items]
Share Of purchased power						84,000,000
Orlando Utilities Commission [Member] \| Southern Power [Member] \| Plant Stanton Combined Cycle Unit [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	28.00%			28.00%
Florida Municipal Power Agency [Member] \| Southern Power [Member] \| Plant Stanton Combined Cycle Unit [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	3.50%			3.50%
Kissimmee Utility Authority [Member] \| Southern Power [Member] \| Plant Stanton Combined Cycle Unit [Member]
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	3.50%			3.50%
Southstar [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage of noncontrolling interest								85.00%
Agreement to purchase remaining interest			$ 160,000,000								$ 160,000,000
Southstar [Member] \| Piedmont [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage of noncontrolling interest								15.00%
Georgia Natural Gas [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Noncontrolling ownership percentage held by parent					100.00%
Piedmont [Member] \| Southstar [Member]
Jointly Owned Utility Plant Interests [Line Items]
Payments of ordinary dividends to noncontrolling interests	$ 15,000,000
Piedmont [Member] \| Southstar [Member] \| Predecessor [Member]
Jointly Owned Utility Plant Interests [Line Items]
Distributions to noncontrolling interests		19,000,000			$ 18,000,000	17,000,000
Southern Natural Gas Company, LLC [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment									50.00%
Horizon Pipeline [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Pipeline infrastructure \| mi	70			70
Horizon Pipeline [Member] \| Successor [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Earnings from equity method investments	$ 1,000,000
Horizon Pipeline [Member] \| Predecessor [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Earnings from equity method investments		1,000,000			2,000,000	$ 2,000,000
PennEast Pipeline [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment						20.00%
Pipeline infrastructure \| mi						118
Atlantic Coast Pipeline [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment						5.00%
Pipeline infrastructure \| mi						594
Atlantic Coast Pipeline [Member] \| Successor [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Earnings from equity method investments	$ 1,000,000
Atlantic Coast Pipeline [Member] \| Predecessor [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Earnings from equity method investments		$ 0			$ 0	$ 0
Pivotal JAX LNG, LLC [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment	50.00%			50.00%
Minimum [Member] \| Horizon Pipeline [Member] \| Nicor Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Capacity of Natural Gas Facility, Percent	70.00%			70.00%
Minimum [Member] \| PennEast Pipeline [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Natural Gas Pipeline Capacity (Volume) \| Bcf						1.0
Minimum [Member] \| Atlantic Coast Pipeline [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Natural Gas Pipeline Capacity (Volume) \| Bcf						1.5
Maximum [Member] \| Horizon Pipeline [Member] \| Nicor Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Capacity of Natural Gas Facility, Percent	80.00%			80.00%
Liquefied Natural Gas (LNG) [Member] \| Pivotal JAX LNG, LLC [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Storage facility capacity \| gal				2,000
Liquefied Natural Gas (LNG) [Member] \| Minimum [Member] \| Pivotal JAX LNG, LLC [Member] \| Southern Company Gas [Member]
Jointly Owned Utility Plant Interests [Line Items]
Storage facility production capacity \| gal				120