Financing - Schedule of Credit Arrangements (Details)	Sep. 30, 2016 USD ($)
Line of Credit Facility [Line Items]
Expires, 2016	$ 150,000,000
Expires, 2017	305,000,000
Expires, 2018	3,590,000,000
Expires, 2020	4,400,000,000
Total	8,445,000,000
Unused	8,281,000,000
Executable Term Loans, One Year	65,000,000
Executable Term Loans, Two Years	15,000,000
Due Within One Year, Term Out	80,000,000
Due Within One Year, No Term Out	300,000,000
Southern Company [Member]
Line of Credit Facility [Line Items]
Expires, 2016	0
Expires, 2017	0
Expires, 2018	1,000,000,000
Expires, 2020	1,250,000,000
Total	2,250,000,000
Unused	2,250,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	0
Alabama Power [Member]
Line of Credit Facility [Line Items]
Expires, 2016	0
Expires, 2017	35,000,000
Expires, 2018	500,000,000
Expires, 2020	800,000,000
Total	1,335,000,000
Unused	1,335,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	35,000,000
Georgia Power [Member]
Line of Credit Facility [Line Items]
Expires, 2016	0
Expires, 2017	0
Expires, 2018	0
Expires, 2020	1,750,000,000
Total	1,750,000,000
Unused	1,732,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	0
Gulf Power [Member]
Line of Credit Facility [Line Items]
Expires, 2016	50,000,000
Expires, 2017	65,000,000
Expires, 2018	165,000,000
Expires, 2020	0
Total	280,000,000
Unused	280,000,000
Executable Term Loans, One Year	45,000,000
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	45,000,000
Due Within One Year, No Term Out	70,000,000
Mississippi Power [Member]
Line of Credit Facility [Line Items]
Expires, 2016	100,000,000
Expires, 2017	75,000,000
Expires, 2018	0
Expires, 2020	0
Total	175,000,000
Unused	150,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	15,000,000
Due Within One Year, Term Out	15,000,000
Due Within One Year, No Term Out	160,000,000
Southern Power [Member]
Line of Credit Facility [Line Items]
Expires, 2016	0
Expires, 2017	0
Expires, 2018	0
Expires, 2020	600,000,000
Total	600,000,000
Unused	532,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	0
Southern Company Gas [Member]
Line of Credit Facility [Line Items]
Expires, 2016	0
Expires, 2017	75,000,000
Expires, 2018	1,925,000,000
Expires, 2020	0
Total	2,000,000,000
Unused	1,947,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	0
Other [Member]
Line of Credit Facility [Line Items]
Expires, 2016	0
Expires, 2017	55,000,000
Expires, 2018	0
Expires, 2020	0
Total	55,000,000
Unused	55,000,000
Executable Term Loans, One Year	20,000,000
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	20,000,000
Due Within One Year, No Term Out	35,000,000
Southern Company Gas Capital [Member]
Line of Credit Facility [Line Items]
Total	$ 1,300,000,000.0