Acquisitions - Acquisitions Table (Details) $ in Millions																			1 Months Ended		6 Months Ended	8 Months Ended	12 Months Ended
	Jan. 06, 2017 MW	Dec. 21, 2016 MW	Dec. 01, 2016 MW	Nov. 16, 2016 MW	Oct. 26, 2016 MW	Aug. 26, 2016 MW	Jul. 01, 2016 MW	Jun. 30, 2016 USD ($) MW	Apr. 07, 2016 MW	Mar. 04, 2016 MW	Feb. 11, 2016 MW	Dec. 11, 2015 MW	Nov. 23, 2015 MW	Oct. 22, 2015 MW	Aug. 31, 2015 MW	Aug. 28, 2015 MW	Apr. 30, 2015 MW	Apr. 15, 2015 MW	Nov. 30, 2016 MW	Jul. 31, 2016 MW	Dec. 31, 2016 USD ($) MW	Jul. 31, 2016 MW	Dec. 31, 2016 USD ($) MW	Dec. 31, 2015 USD ($)	Mar. 29, 2016	Dec. 17, 2015 MW	Dec. 31, 2014 USD ($)
Purchase Price Allocation
Goodwill																					$ 6,251		$ 6,251	$ 2
Acquisition Information, by Acquisition [Abstract]
Assets																					109,697		109,697	78,318			$ 70,233
PowerSecure International, Inc. [Member]
Purchase Price Allocation
Current assets																					172		172
Property, plant, and equipment																					46		46
Goodwill																					101		101
Intangible assets																					282		282
Other assets																					4		4
Current liabilities																					(114)		(114)
Long-term debt, including current portion																					48		48
Other liabilities																					(14)		(14)
Total purchase price																					429		429
Southern Power [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability																					46		46	36
Purchase Price Allocation
Total purchase price																					2,603		2,603	$ 1,931
Acquisition Information, by Acquisition [Abstract]
Life Output Of Plant																								20 years
Assets																					15,169		$ 15,169	$ 8,905
Southern Power [Member] | Boulder 1 [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW				100
Noncontrolling Interest, Ownership Percentage by Parent				51.00%
Life Output Of Plant				20 years
Southern Power [Member] | 70SM1 8ME, LCC (Calipatria) [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW											20
Noncontrolling Interest, Ownership Percentage by Parent											90.00%
Life Output Of Plant											20 years
Southern Power [Member] | East Pecos [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW										120
Noncontrolling Interest, Ownership Percentage by Parent										100.00%
Life Output Of Plant										15 years
Southern Power [Member] | Grant Plains [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW						147
Noncontrolling Interest, Ownership Percentage by Parent						100.00%
Life Output Of Plant						12 years
Southern Power [Member] | Grant Wind, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW									151
Noncontrolling Interest, Ownership Percentage by Parent									100.00%
Life Output Of Plant									20 years
Southern Power [Member] | Henrietta [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW							102
Noncontrolling Interest, Ownership Percentage by Parent							51.00%
Life Output Of Plant							20 years
Southern Power [Member] | Lamesa [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW							102
Noncontrolling Interest, Ownership Percentage by Parent							100.00%
Life Output Of Plant							15 years
Southern Power [Member] | Mankato [Member]
Acquisition Information, by Acquisition [Abstract]
Capacity of Natural Gas Facility | MW					375
Noncontrolling Interest, Ownership Percentage by Parent					100.00%
Life Output Of Plant					10 years																		10 years
Southern Power [Member] | Passadumkeag, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW								42
Noncontrolling Interest, Ownership Percentage by Parent								100.00%
Life Output Of Plant								15 years
Southern Power [Member] | Rutherford [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW							74
Noncontrolling Interest, Ownership Percentage by Parent							90.00%
Life Output Of Plant							15 years
Southern Power [Member] | Salt Fork [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW			174
Noncontrolling Interest, Ownership Percentage by Parent			100.00%
Southern Power [Member] | Tyler Bluff [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW		125
Noncontrolling Interest, Ownership Percentage by Parent		100.00%
Life Output Of Plant		12 years
Southern Power [Member] | Wake Wind [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW					257
Noncontrolling Interest, Ownership Percentage by Parent					90.10%
Life Output Of Plant					12 years
Southern Power [Member] | Series of Business Acquisitions [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability																					281		$ 281	195
Purchase Price Allocation
CWIP																					2,354		2,354	1,367
Property, plant, and equipment																					302		302	315
Intangible assets																					128		128	274
Other assets																					52		52	64
Accounts payable																					(16)		(16)	(89)
Debt																					(217)		(217)
Total purchase price																					$ 2,345		$ 2,345	$ 1,440
Southern Power [Member] | Desert Stateline Holdings, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW															299					299	299	299	299
Noncontrolling Interest, Ownership Percentage by Parent															51.00%										15.00%
Life Output Of Plant															20 years							20 years
Southern Power [Member] | RE Garland and Garland A Holdings, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW																										205
Noncontrolling Interest, Ownership Percentage by Parent																										51.00%
Southern Power [Member] | Kay Wind, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW												299
Noncontrolling Interest, Ownership Percentage by Parent												100.00%
Life Output Of Plant												20 years
Southern Power [Member] | Lost Hills Blackwell Holdings, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW																		33
Noncontrolling Interest, Ownership Percentage by Parent																		51.00%
Life Output Of Plant																		29 years
Southern Power [Member] | GASNA 31P, LLC (Morelos) [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW														15
Noncontrolling Interest, Ownership Percentage by Parent														90.00%
Life Output Of Plant														20 years
Southern Power [Member] | NS Solar Holdings, LLC (North Star) [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW																	61
Noncontrolling Interest, Ownership Percentage by Parent																	51.00%
Life Output Of Plant																	20 years
Southern Power [Member] | RE Roserock Holdings, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW													160						160
Noncontrolling Interest, Ownership Percentage by Parent													51.00%
Life Output Of Plant													20 years						20 years
Southern Power [Member] | RE Tranquility Holdings, LLC [Member]
Acquisition Information, by Acquisition [Abstract]
Power of Solar Polycrystalline Silicon Facility | MW																205				205		205
Noncontrolling Interest, Ownership Percentage by Parent																51.00%
Life Output Of Plant																18 years				18 years
Turner Renewable Energy [Member] | 70SM1 8ME, LCC (Calipatria) [Member]
Acquisition Information, by Acquisition [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent											10.00%
Turner Renewable Energy [Member] | Rutherford [Member]
Acquisition Information, by Acquisition [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent							10.00%
Turner Renewable Energy [Member] | GASNA 31P, LLC (Morelos) [Member]
Acquisition Information, by Acquisition [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent														10.00%										10.00%
Noncontrolling Interests [Member] | Series of Business Acquisitions [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability																					$ 142		$ 142	$ 76
Purchase Price Allocation
Total purchase price																					258		258	$ 491
Successor [Member] | Southern Company Gas [Member]
Purchase Price Allocation
Current assets																					1,557		1,557
Property, plant, and equipment																					10,108		10,108
Goodwill																					5,967		5,967
Intangible assets																					400		400
Regulatory assets																					1,118		1,118
Other assets																					229		229
Current liabilities																					(2,201)		(2,201)
Other liabilities																					(4,742)		(4,742)
Long-term debt																					(4,261)		(4,261)
Noncontrolling interests																					(174)		(174)
Total purchase price																					8,001		8,001
Predecessor [Member] | Southern Company Gas [Member]
Purchase Price Allocation
Current assets								$ 1,474
Property, plant, and equipment								10,148
Goodwill								1,813
Intangible assets								101
Regulatory assets								679
Other assets								273
Current liabilities								(2,205)
Other liabilities								(4,600)
Long-term debt								(3,709)
Noncontrolling interests								(41)
Total purchase price								$ 3,933
Change in Basis
Current assets																					83
Property, plant, and equipment																					(40)
Goodwill																					4,154
Other intangible assets																					299
Regulatory assets																					439
Other assets																					(44)
Current liabilities																					4
Other liabilities																					(142)
Long-term debt																					(552)
Contingently redeemable noncontrolling interest																					(133)
Total purchase price/equity																					4,068
Subsequent Event [Member] | Southern Power [Member] | Bethel [Member]
Acquisition Information, by Acquisition [Abstract]
Energy From Wind-Powered Generating Facilities | MW	276
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Life Output Of Plant	12 years
Grant County [Member] | Southern Power [Member] | Grant Plains [Member]
Acquisition Information, by Acquisition [Abstract]
Life Output Of Plant						20 years
Donley County [Member] | Southern Power [Member] | Salt Fork [Member]
Acquisition Information, by Acquisition [Abstract]
Life Output Of Plant			14 years
Gray County [Member] | Southern Power [Member] | Salt Fork [Member]
Acquisition Information, by Acquisition [Abstract]
Life Output Of Plant			12 years
Payables [Member] | Southern Power [Member] | Series of Business Acquisitions [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability																					67		67
Senior Lien [Member] | Southern Power [Member]
Acquisition Information, by Acquisition [Abstract]
Assets																					$ 408		$ 408