Summary of Significant Accounting Policies - Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 3,759	$ 2,201
Liabilities incurred	66	662
Liabilities settled	(171)	(37)
Accretion	162	115
Cash flow revisions	698	818
Balance at end of year	4,514	3,759
Alabama Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	1,448	829
Liabilities incurred	5	402
Liabilities settled	(25)	(3)
Accretion	73	53
Cash flow revisions	32	167
Balance at end of year	1,533	1,448
Georgia Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	1,916	1,255
Liabilities incurred	0	6
Liabilities settled	(123)	(30)
Accretion	77	56
Cash flow revisions	662	629
Balance at end of year	2,532	1,916
Gulf Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	130	17
Liabilities incurred	1	105
Liabilities settled	(1)	(1)
Accretion	4	2
Cash flow revisions	2	7
Balance at end of year	136	130
Mississippi Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	177	48
Liabilities incurred	15	101
Liabilities settled	(23)	(3)
Accretion	5	4
Cash flow revisions	5	27
Balance at end of year	179	177
Southern Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	21	13
Liabilities incurred	42	7
Accretion	1	1
Balance at end of year	64	21
Plant Scholz | Gulf Power [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 29
Balance at end of year		$ 29