Summary of Significant Accounting Policies - Affiliate Transactions (Details)						4 Months Ended	6 Months Ended	12 Months Ended
	Dec. 14, 2016 USD ($)	Oct. 04, 2016 USD ($)	Jun. 27, 2016 USD ($)	Jan. 28, 2016 USD ($)	Jun. 03, 2015 USD ($)	Dec. 31, 2016 USD ($) location	Dec. 31, 2016 USD ($) location	Dec. 31, 2016 USD ($) location	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 01, 2016
Related Party Transaction [Line Items]
Long-term Debt and Capital Lease Obligations, Current						$ 2,587,000,000	$ 2,587,000,000	$ 2,587,000,000	$ 2,674,000,000
Alabama Power [Member]
Related Party Transaction [Line Items]
Ownership percentage, equity method investment						50.00%	50.00%	50.00%
Capital contributions from parent company								$ 260,000,000	22,000,000	$ 28,000,000
Long-term Debt and Capital Lease Obligations, Current						$ 561,000,000	$ 561,000,000	561,000,000	200,000,000
Mississippi Power [Member]
Related Party Transaction [Line Items]
Capital contributions from parent company	$ 400,000,000		$ 225,000,000					627,000,000	277,000,000	451,000,000
Issuance of Promissory note to parent related to repayment of interest-bearing refundable deposits and accrued interest				$ 275,000,000	$ 301,000,000			0	301,000,000	0
Long-term Debt and Capital Lease Obligations, Current						629,000,000	629,000,000	629,000,000	728,000,000
Long-term debt affiliated						551,000,000	551,000,000	551,000,000	0
Gulf Power [Member]
Related Party Transaction [Line Items]
Capital contributions from parent company								20,000,000	4,000,000	4,000,000
Long-term Debt and Capital Lease Obligations, Current						87,000,000	87,000,000	87,000,000	110,000,000
Southern Power [Member]
Related Party Transaction [Line Items]
Deferred Project Development Costs									11,000,000
Capital contributions from parent company								1,850,000,000	646,000,000	146,000,000
Long-term Debt and Capital Lease Obligations, Current						$ 560,000,000	$ 560,000,000	$ 560,000,000	403,000,000
Georgia Power [Member]
Related Party Transaction [Line Items]
Number Of Military Bases For Renewable Generation | location						2	2	2
Capital contributions from parent company								$ 594,000,000	62,000,000	549,000,000
Long-term Debt and Capital Lease Obligations, Current						$ 460,000,000	$ 460,000,000	460,000,000	712,000,000
PowerSecure International, Inc. [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount		$ 118,000,000
Southern Natural Gas Company, LLC [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount						2,000,000
Southern Natural Gas Company, LLC [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Related party transaction, amount						15,000,000
Southern Natural Gas Company, LLC [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount						7,000,000
Southern Natural Gas Company, LLC [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount						$ 35,000,000
Southern Company Services, Inc. [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								460,000,000	438,000,000	400,000,000
Southern Company Services, Inc. [Member] | Mississippi Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								231,000,000	295,000,000	259,000,000
Southern Company Services, Inc. [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								80,000,000	81,000,000	80,000,000
Southern Company Services, Inc. [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								193,000,000	146,000,000	126,000,000
Southern Company Services, Inc. [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								606,000,000	585,000,000	555,000,000
Georgia Power [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								8,000,000	12,000,000	9,000,000
Mississippi Power [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								26,000,000	27,000,000	31,000,000
Alabama Power [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Revenue requirements reimbursement								12,000,000	14,000,000	12,000,000
Gulf Power [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Revenue requirements reimbursement								12,000,000	14,000,000	12,000,000
Gulf Power [Member] | Mississippi Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								26,000,000	27,000,000	31,000,000
Gulf Power [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								$ 7,000,000
Gulf Power [Member] | Georgia Power [Member] | Plant Scherer Unit Three [Member]
Related Party Transaction [Line Items]
Long-term Purchase Commitment, Reimbursement Percentage						25.00%	25.00%	25.00%
Southern Company Gas [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount							$ 17,000,000
Southern Company Gas [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount						$ 10,000,000
Southern Power [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								$ 6,800,000
Southern Power [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								265,000,000	179,000,000	144,000,000
Southern Nuclear Operating Company, Inc. [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								249,000,000	243,000,000	234,000,000
Southern Nuclear Operating Company, Inc. [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								666,000,000	681,000,000	643,000,000
Successor [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Capital contributions from parent company							1,085,000,000
Long-term Debt and Capital Lease Obligations, Current						$ 22,000,000	22,000,000	22,000,000
Successor [Member] | Southern Company Services, Inc. [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Related party transaction, amount							17,000,000
Successor [Member] | Southern Company Services, Inc. [Member] | Southstar [Member]
Related Party Transaction [Line Items]
Revenue from related parties							9,000,000
Successor [Member] | Southern Company Services, Inc. [Member] | Sequent [Member]
Related Party Transaction [Line Items]
Revenue from related parties							$ 19,000,000
Scenario, Plan [Member] | Alabama Power [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Revenue requirements reimbursement								10,000,000
Scenario, Plan [Member] | Gulf Power [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Revenue requirements reimbursement								73,000,000
Southern Natural Gas Company, LLC [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Ownership percentage, equity method investment											50.00%
Non-Fuel Expense [Member] | Mississippi Power [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								13,000,000	11,000,000	13,000,000
Non-Fuel Expense [Member] | Alabama Power [Member] | Mississippi Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								13,000,000	11,000,000	13,000,000
Non-Fuel Expense [Member] | Gulf Power [Member] | Georgia Power [Member] | Plant Scherer Unit Three [Member]
Related Party Transaction [Line Items]
Reimbursement Revenue								8,000,000	12,000,000	9,000,000
Fuel Purchases [Member] | Mississippi Power [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								0	8,000,000	34,000,000
Fuel Purchases [Member] | Alabama Power [Member] | Mississippi Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount									8,000,000	34,000,000
Purchased Power from Affiliates [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								258,000,000	219,000,000	153,000,000
Operating Lease PPA [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								109,000,000	109,000,000	75,000,000
Operations and Maintenance Expense [Member] | Southern Company Services, Inc. [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								173,000,000	$ 138,000,000	125,000,000
Electric Transmission [Member] | Southern Company Services, Inc. [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transaction, amount								$ 11,000,000		$ 7,000,000