Financing - Narrative (Details) - USD ($)				1 Months Ended	3 Months Ended
	Feb. 28, 2017	Jun. 03, 2015	Feb. 20, 2014	Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Short-term debt				$ 2,818,000,000	$ 2,818,000,000	$ 2,241,000,000
Variable rate pollution control revenue bonds outstanding				1,900,000,000	1,900,000,000
Maximum borrowing capacity				8,443,000,000	8,443,000,000
Senior Note Issuances					1,400,000,000
Mississippi Power [Member]
Debt Instrument [Line Items]
Working capital				1,200,000,000	1,200,000,000
Senior notes, current				35,000,000	35,000,000
Short-term debt				36,000,000	36,000,000	23,000,000
Long-term pollution control bond				50,000,000	50,000,000
Variable rate pollution control revenue bonds outstanding				40,000,000	40,000,000
Fixed rate pollution control revenue bonds outstanding				50,000,000	50,000,000
Maximum borrowing capacity				173,000,000	173,000,000
Promissory note		$ 301,000,000
Mississippi Power [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Short-term debt				36,000,000	36,000,000
Mississippi Power [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Loans payable to bank				1,200,000,000	1,200,000,000
Mississippi Power [Member] | Tax-Exempt Variable Rate Demand Obligations [Member]
Debt Instrument [Line Items]
Short-term debt				40,000,000	40,000,000
Mississippi Power [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Debt face amount				$ 9,000,000	$ 9,000,000
Debt stated interest rate				5.00%	5.00%
Georgia Power [Member]
Debt Instrument [Line Items]
Short-term debt				$ 0	$ 0	391,000,000
Debt instrument, basis spread on variable rate			0.375%
Amortization period for line of credit facility			5 years
Variable rate pollution control revenue bonds outstanding				868,000,000	868,000,000
Fixed rate pollution control revenue bonds outstanding				250,000,000	250,000,000
Maximum borrowing capacity				1,750,000,000	1,750,000,000
Senior Note Issuances					850,000,000
Georgia Power [Member] | Senior Notes [Member] | Series 2017A [Member]
Debt Instrument [Line Items]
Debt face amount				$ 450,000,000	$ 450,000,000
Debt stated interest rate				2.00%	2.00%
Georgia Power [Member] | Senior Notes [Member] | Series 2017B [Member]
Debt Instrument [Line Items]
Debt face amount				$ 400,000,000	$ 400,000,000
Debt stated interest rate				3.25%	3.25%
Alabama Power [Member]
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding				$ 890,000,000	$ 890,000,000
Maximum borrowing capacity				1,335,000,000	1,335,000,000
Senior Note Issuances					550,000,000
Alabama Power [Member] | Senior Notes [Member] | Series 2017A [Member]
Debt Instrument [Line Items]
Debt face amount				$ 550,000,000	$ 550,000,000
Debt stated interest rate				2.45%	2.45%
Gulf Power [Member]
Debt Instrument [Line Items]
Short-term debt				$ 100,000,000	$ 100,000,000	268,000,000
Variable rate pollution control revenue bonds outstanding				82,000,000	82,000,000
Fixed rate pollution control revenue bonds outstanding				86,000,000	86,000,000
Maximum borrowing capacity				280,000,000	280,000,000
Senior Note Issuances					0
Gulf Power [Member] | Bank Loans [Member]
Debt Instrument [Line Items]
Debt face amount				100,000,000	100,000,000
Traditional Operating Companies [Member]
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding				386,000,000	386,000,000
Southern Power [Member]
Debt Instrument [Line Items]
Short-term debt				380,000,000	380,000,000	$ 209,000,000
Maximum borrowing capacity				600,000,000	600,000,000
Senior Note Issuances					0
Southern Company [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				2,250,000,000	2,250,000,000
Senior Note Issuances					$ 0
Southern Company [Member] | Bank Loans [Member]
Debt Instrument [Line Items]
Senior Note Issuances				$ 400,000,000
Debt Instrument, Term				18 months
Southern Company [Member] | Mississippi Power [Member]
Debt Instrument [Line Items]
Promissory note	$ 551,000,000