Financing - Schedule of Long-Term Debt Financing Activities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Senior Note Issuances	$ 2,950
Senior Note Maturities and Redemptions	1,135
Revenue Bond Maturities, Redemptions, and Repurchases	101
Other Long-Term Debt Issuances	1,119
Other Long-Term Debt Redemptions and Maturities	745
Southern Company
Debt Instrument [Line Items]
Senior Note Issuances	300
Senior Note Maturities and Redemptions	400
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	500
Other Long-Term Debt Redemptions and Maturities	400
ALABAMA POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	550
Senior Note Maturities and Redemptions	200
Revenue Bond Maturities, Redemptions, and Repurchases	36
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	0
GEORGIA POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	1,350
Senior Note Maturities and Redemptions	450
Revenue Bond Maturities, Redemptions, and Repurchases	65
Other Long-Term Debt Issuances	370
Other Long-Term Debt Redemptions and Maturities	13
GULF POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	300
Senior Note Maturities and Redemptions	85
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	6
Other Long-Term Debt Redemptions and Maturities	0
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	40
Other Long-Term Debt Redemptions and Maturities	893
SOUTHERN POWER CO
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	43
Other Long-Term Debt Redemptions and Maturities	4
SOUTHERN Co GAS
Debt Instrument [Line Items]
Senior Note Issuances	450
Senior Note Maturities and Redemptions	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	200
Other Long-Term Debt Redemptions and Maturities	22
Other
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	0
Other Long-Term Debt Redemptions and Maturities	12
Elimination
Debt Instrument [Line Items]
Senior Note Issuances	0
Senior Note Maturities and Redemptions	0
Revenue Bond Maturities, Redemptions, and Repurchases	0
Other Long-Term Debt Issuances	(40)
Other Long-Term Debt Redemptions and Maturities	$ (599)