Derivatives - Narrative (Details) MMBTU in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) MMBTU	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Collateral already posted, aggregate fair value	$ 71,000,000
Maximum potential collateral requirements arising from credit risk related contingent features	$ 11,000,000
Southern Company
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	31
Cash flow hedge gain (loss) to be reclassified within twelve months	$ (21,000,000)
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	10
SOUTHERN POWER CO
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	$ 6,000,000
Gulf Power and Mississippi Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	3
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	5
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	$ (23,000,000)
SOUTHERN Co GAS
Derivative [Line Items]
Collateral already posted, aggregate fair value	71,000,000	$ 62,000,000
Maximum potential collateral requirements arising from credit risk related contingent features	1,000,000
Traditional Operating Companies and Southern Power
Derivative [Line Items]
Maximum potential collateral requirements arising from credit risk related contingent features	10,000,000
Derivative Counterparties | Registrants
Derivative [Line Items]
Collateral already posted, aggregate fair value	$ 0