Financing - Schedule of Long-Term Debt Financing Activities (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Aug. 31, 2015	Sep. 30, 2015
Debt Instrument [Line Items]
Senior Note Issuances		$ 2,225.0
Senior Note Redemptions		1,760.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		367.0
Revenue Bond Maturities and Repurchases		415.0
Other Long-Term Debt Issuances		1,400.0
Other Long-Term Debt Redemptions and Maturities		388.0
Southern Company [Member]
Debt Instrument [Line Items]
Senior Note Issuances		600.0
Senior Note Redemptions		400.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		0.0
Revenue Bond Maturities and Repurchases		0.0
Other Long-Term Debt Issuances		400.0
Other Long-Term Debt Redemptions and Maturities		0.0
Alabama Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances		975.0
Senior Note Redemptions		250.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		80.0
Revenue Bond Maturities and Repurchases		134.0
Other Long-Term Debt Issuances		0.0
Other Long-Term Debt Redemptions and Maturities		0.0
Alabama Power [Member] | Debt Held Since 2015 [Member]
Debt Instrument [Line Items]
Revenue Bond Issuances and Reofferings of Purchased Bonds		80.0
Georgia Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances		0.0
Senior Note Redemptions		525.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		274.0
Revenue Bond Maturities and Repurchases		268.0
Other Long-Term Debt Issuances		600.0
Other Long-Term Debt Redemptions and Maturities		20.0
Georgia Power [Member] | Debt Held Since 2015 [Member]
Debt Instrument [Line Items]
Revenue Bond Issuances and Reofferings of Purchased Bonds		65.0
Georgia Power [Member] | Debt Held Since 2009 [Member]
Debt Instrument [Line Items]
Revenue Bond Issuances and Reofferings of Purchased Bonds	$ 94.6
Georgia Power [Member] | Debt Held Since 2013 [Member]
Debt Instrument [Line Items]
Revenue Bond Issuances and Reofferings of Purchased Bonds	$ 10.0	104.6
Gulf Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances		0.0
Senior Note Redemptions		60.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		13.0
Revenue Bond Maturities and Repurchases		13.0
Other Long-Term Debt Issuances		0.0
Other Long-Term Debt Redemptions and Maturities		0.0
Gulf Power [Member] | Debt Held Since 2015 [Member]
Debt Instrument [Line Items]
Revenue Bond Issuances and Reofferings of Purchased Bonds		13.0
Mississippi Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances		0.0
Senior Note Redemptions		0.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		0.0
Revenue Bond Maturities and Repurchases		0.0
Other Long-Term Debt Issuances		0.0
Other Long-Term Debt Redemptions and Maturities		352.0
Southern Power [Member]
Debt Instrument [Line Items]
Senior Note Issuances		650.0
Senior Note Redemptions		525.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		0.0
Revenue Bond Maturities and Repurchases		0.0
Other Long-Term Debt Issuances		400.0
Other Long-Term Debt Redemptions and Maturities		3.0
Other [Member]
Debt Instrument [Line Items]
Senior Note Issuances		0.0
Senior Note Redemptions		0.0
Revenue Bond Issuances and Reofferings of Purchased Bonds		0.0
Revenue Bond Maturities and Repurchases		0.0
Other Long-Term Debt Issuances		0.0
Other Long-Term Debt Redemptions and Maturities		$ 13.0