Derivatives - Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Depreciation and amortization	$ 783	$ 754	$ 1,552	$ 1,469
Interest expense, net of amounts capitalized	(470)	(424)	(928)	(840)
Other income (expense), net	78	52	138	98
Cost of natural gas	228	232	949	951
Other income (expense), net | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(73)	79	(37)	96
Cash Flow Hedging | Depreciation and amortization | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	1	(2)	2	(6)
Cash Flow Hedging | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(6)	(5)	(11)	(10)
Cash Flow Hedging | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(7)	(5)	(12)	(12)
Cash Flow Hedging | Cost of natural gas | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	0	0	(2)	0
Fair Value Hedging | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(7)	7	(31)	(1)
ALABAMA POWER CO
Derivative [Line Items]
Depreciation and amortization	189	183	379	364
Interest expense, net of amounts capitalized	(80)	(77)	(158)	(153)
Other income (expense), net	12	15	15	25
ALABAMA POWER CO | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(1)	(2)	(3)	(3)
GEORGIA POWER CO
Derivative [Line Items]
Depreciation and amortization	230	223	458	444
Interest expense, net of amounts capitalized	(102)	(104)	(208)	(205)
Other income (expense), net	35	34	73	71
GEORGIA POWER CO | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(2)	(1)	(3)	(3)
GEORGIA POWER CO | Fair Value Hedging | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	2	0	(1)	(1)
MISSISSIPPI POWER CO
Derivative [Line Items]
Depreciation and amortization	44	41	84	81
Interest expense, net of amounts capitalized	(21)	(17)	(39)	(37)
Other income (expense), net	27	3	27	5
MISSISSIPPI POWER CO | Interest expense, net of amounts capitalized | Interest rate derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(1)	0	(1)	(1)
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	125	129	240	247
Interest expense, net of amounts capitalized	(46)	(48)	(93)	(97)
Other income (expense), net	2	2	5	(2)
SOUTHERN POWER CO | Cash Flow Hedging | Depreciation and amortization | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	1	(2)	2	(6)
SOUTHERN POWER CO | Cash Flow Hedging | Interest expense, net of amounts capitalized | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(7)	(5)	(12)	(12)
SOUTHERN POWER CO | Cash Flow Hedging | Other income (expense), net | Foreign currency derivatives
Derivative [Line Items]
Gain (loss) recognized in income	(73)	79	(37)	96
SOUTHERN Co GAS
Derivative [Line Items]
Depreciation and amortization	126	125	255	244
Interest expense, net of amounts capitalized	(59)	(48)	(118)	(94)
Other income (expense), net	3	4	15	10
Cost of natural gas	228	232	949	951
SOUTHERN Co GAS | Cost of natural gas | Energy-related derivatives
Derivative [Line Items]
Gain (loss) recognized in income	$ 0	$ 0	$ (2)	$ 0