Stockholders' Equity - Changes in Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in Stockholders' Equity
Beginning balance, treasury shares (in shares)			(900)
Beginning balance			$ 25,528	$ 26,612
Consolidated net income attributable to Southern Company	$ (154)	$ (1,381)	784	(723)
Other comprehensive income			41	(11)
Stock issued			222	417
Stock-based compensation			48	72
Cash dividends on common stock			(1,194)	(1,134)
Preference stock redemption				(150)
Contributions from noncontrolling interests			31	71
Distributions to noncontrolling interests			(42)	(40)
Net income attributable to noncontrolling interests			17	16
Sale of SPSH noncontrolling interests			1,283
Reclassification from redeemable noncontrolling interests				114
Other			$ (26)	(3)
Ending balance, treasury shares (in shares)	(1,000)		(1,000)
Ending balance	$ 26,692	$ 25,241	$ 26,692	$ 25,241
Number of Common Shares Issued
Changes in Stockholders' Equity
Beginning balance (in shares)			1,008,532	991,213
Stock issued (in shares)			6,590	9,129
Other (in shares)			0
Ending balance (in shares)	1,015,122	1,000,342	1,015,122	1,000,342
Number of Common Shares Treasury Issued
Changes in Stockholders' Equity
Beginning balance, treasury shares (in shares)			(929)	(819)
Stock issued (in shares)			0	0
Other (in shares)			(57)	(49)
Ending balance, treasury shares (in shares)	(986)	(868)	(986)	(868)
Common Stockholders' Equity
Changes in Stockholders' Equity
Beginning balance			$ 24,167	$ 24,758
Consolidated net income attributable to Southern Company			784	(723)
Other comprehensive income			41	(11)
Stock issued			222	417
Stock-based compensation			48	72
Cash dividends on common stock			(1,194)	(1,134)
Sale of SPSH noncontrolling interests			(407)
Other			(25)	(7)
Ending balance	$ 23,636	$ 23,372	23,636	23,372
Preferred and Preference Stock of Subsidiaries
Changes in Stockholders' Equity
Beginning balance			0	609
Preference stock redemption				(150)
Other			0	3
Ending balance	0	462	0	462
Noncontrolling Interest
Changes in Stockholders' Equity
Beginning balance			1,361	1,245
Contributions from noncontrolling interests			31	71
Distributions to noncontrolling interests			(42)	(40)
Net income attributable to noncontrolling interests			17	16
Sale of SPSH noncontrolling interests			1,690
Reclassification from redeemable noncontrolling interests				114
Other			(1)	1
Ending balance	$ 3,056	$ 1,407	$ 3,056	$ 1,407