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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Depreciation and amortization	$ 760	$ 787	$ 2,267	$ 2,338
Total interest expense, net of amounts capitalized	(434)	(458)	(1,294)	(1,386)
Total other income (expense), net	61	57	239	195
Cash Flow Hedging | Gain (loss) on energy-related cash flow hedges | Total depreciation and amortization
Derivative [Line Items]
Gain (loss) on hedge	(1)	0	(5)	2
Cash Flow Hedging | Interest rate derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(5)	(5)	(14)	(16)
Cash Flow Hedging | Foreign currency derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(6)	(18)	(18)
Cash Flow Hedging | Foreign currency derivatives | Total other income (expense), net
Derivative [Line Items]
Gain (loss) on hedge	(54)	(9)	(62)	(46)
Fair Value Hedging | Interest rate derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	10	(4)	43	(35)
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	120	130	357	370
Total interest expense, net of amounts capitalized	(43)	(45)	(127)	(138)
Total other income (expense), net	6	17	48	22
SOUTHERN POWER CO | Cash Flow Hedging | Gain (loss) on energy-related cash flow hedges | Total depreciation and amortization
Derivative [Line Items]
Gain (loss) on hedge	(1)	0	(5)	2
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(6)	(18)	(18)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Total other income (expense), net
Derivative [Line Items]
Gain (loss) on hedge	$ (54)	$ (9)	$ (62)	$ (46)