Financing - Schedule of Credit Arrangements (Details)	Mar. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Expires, 2017	$ 423,000,000
Expires, 2018	3,620,000,000
Expires, 2020	4,400,000,000
Total	8,443,000,000
Unused	8,266,000,000
Executable Term Loans, One Year	65,000,000
Executable Term Loans, Two Years	13,000,000
Expires Within One Year, Term Out	58,000,000
Expires Within One Year, No Term Out	375,000,000
Southern Company [Member]
Line of Credit Facility [Line Items]
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
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Alabama Power [Member]
Line of Credit Facility [Line Items]
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
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	35,000,000
Georgia Power [Member]
Line of Credit Facility [Line Items]
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
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Gulf Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	85,000,000
Expires, 2018	195,000,000
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
Expires Within One Year, Term Out	25,000,000
Expires Within One Year, No Term Out	70,000,000
Mississippi Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	173,000,000
Expires, 2018	0
Expires, 2020	0
Total	173,000,000
Unused	141,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	13,000,000
Expires Within One Year, Term Out	13,000,000
Expires Within One Year, No Term Out	160,000,000
Southern Power [Member]
Line of Credit Facility [Line Items]
Expires, 2017	0
Expires, 2018	0
Expires, 2020	600,000,000
Total	600,000,000
Unused	524,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	0
Southern Company Gas [Member]
Line of Credit Facility [Line Items]
Expires, 2017	75,000,000
Expires, 2018	1,925,000,000
Expires, 2020	0
Total	2,000,000,000
Unused	1,949,000,000
Executable Term Loans, One Year	0
Executable Term Loans, Two Years	0
Expires Within One Year, Term Out	0
Expires Within One Year, No Term Out	75,000,000
Other [Member]
Line of Credit Facility [Line Items]
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
Expires Within One Year, Term Out	20,000,000
Expires 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
Nicor Gas [Member]
Line of Credit Facility [Line Items]
Total	$ 700,000,000