Financing - Schedule of Credit Arrangements (Details)	Sep. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Expires, 2015	$ 35,000,000
Expires, 2016	555,000,000
Expires, 2017	30,000,000
Expires, 2018	1,500,000,000
Expires, 2020	4,400,000,000
Total	6,520,000,000
Unused	6,443,000,000
Executable Term Loans, One Year	80,000,000
Executable Term Loans, Two Years	30,000,000
Due Within One Year, Term Out	110,000,000
Due Within One Year, No Term Out	480,000,000
Southern Company [Member]
Line of Credit Facility [Line Items]
Expires, 2015	0
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, 2015	0
Expires, 2016	40,000,000
Expires, 2017	0
Expires, 2018	500,000,000
Expires, 2020	800,000,000
Total	1,340,000,000
Unused	1,339,000,000
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	40,000,000
Georgia Power [Member]
Line of Credit Facility [Line Items]
Expires, 2015	0
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, 2015	20,000,000
Expires, 2016	225,000,000
Expires, 2017	30,000,000
Expires, 2018	0
Expires, 2020	0
Total	275,000,000
Unused	275,000,000
Executable Term Loans, One Year	50,000,000
Executable Term Loans, Two Years	0
Due Within One Year, Term Out	50,000,000
Due Within One Year, No Term Out	195,000,000
Mississippi Power [Member]
Line of Credit Facility [Line Items]
Expires, 2015	15,000,000
Expires, 2016	220,000,000
Expires, 2017	0
Expires, 2018	0
Expires, 2020	0
Total	235,000,000
Unused	210,000,000
Executable Term Loans, One Year	30,000,000
Executable Term Loans, Two Years	30,000,000
Due Within One Year, Term Out	60,000,000
Due Within One Year, No Term Out	175,000,000
Southern Power [Member]
Line of Credit Facility [Line Items]
Expires, 2015	0
Expires, 2016	0
Expires, 2017	0
Expires, 2018	0
Expires, 2020	600,000,000
Total	600,000,000
Unused	567,000,000
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, 2015	0
Expires, 2016	70,000,000
Expires, 2017	0
Expires, 2018	0
Expires, 2020	0
Total	70,000,000
Unused	70,000,000
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	70,000,000
Scenario, Plan [Member] | Bridge Agreement [Member]
Line of Credit Facility [Line Items]
Total	$ 8,100,000,000.0