Financing - Committed Credit Arrangements With Banks (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2015
Credit arrangements by company
Expires, 2017	$ 423
Expires, 2018	3,620
Expires, 2020	4,400
Total	8,443
Unused	8,273
Executable Term-Loans, One Year	65
Executable Term-Loans, Two Years	13
Due Within One Year, Term Out	58
Due Within One Year, No Term Out	365
Southern Company Gas Capital [Member]
Credit arrangements by company
Expires, 2017	49
Expires, 2018	1,251
Total	1,300
Unused	1,249
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	49
Southern Company [Member]
Credit arrangements by company
Expires, 2017	0
Expires, 2018	1,000
Expires, 2020	1,250
Total	2,250
Unused	2,250
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]
Credit arrangements by company
Expires, 2017	35
Expires, 2018	500
Expires, 2020	800
Total	1,335
Unused	1,335
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
Georgia Power [Member]
Credit arrangements by company
Expires, 2017	0
Expires, 2018	0
Expires, 2020	1,750
Total	1,750
Unused	1,732
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]
Credit arrangements by company
Expires, 2017	85
Expires, 2018	195
Expires, 2020	0
Total	280
Unused	280
Executable Term-Loans, One Year	45
Executable Term-Loans, Two Years	0
Due Within One Year, Term Out	25
Due Within One Year, No Term Out	60
Gulf Power [Member]
Credit arrangements by company
Expires, 2017	75
Expires, 2018	1,925
Expires, 2020	0
Total	2,000
Unused	1,949
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	75
Nicor Gas [Member]
Credit arrangements by company
Expires, 2017	26
Expires, 2018	674
Total	700
Unused	700
Due Within One Year, Term Out	0
Due Within One Year, No Term Out	26
Mississippi Power [Member]
Credit arrangements by company
Expires, 2017	173
Expires, 2018	0
Expires, 2020	0
Total	173
Unused	150
Executable Term-Loans, One Year	0
Executable Term-Loans, Two Years	13
Due Within One Year, Term Out	13
Due Within One Year, No Term Out	160
Southern Power [Member]
Credit arrangements by company
Expires, 2017	0
Expires, 2018	0
Expires, 2020	600
Total	600		$ 600
Unused	522	$ 566
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 Subsidiaries [Member]
Credit arrangements by company
Expires, 2017	55
Expires, 2018	0
Expires, 2020	0
Total	55
Unused	55
Executable Term-Loans, One Year	20
Executable Term-Loans, Two Years	0
Due Within One Year, Term Out	20
Due Within One Year, No Term Out	35
Continuing Letter of Credit Facility [Member] | Southern Power [Member]
Credit arrangements by company
Total	120
Unused	$ 82