Derivatives - Textual (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) MMBTU
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	5,000,000
Fair value of derivative liabilities with contingent features	$ 52
Maximum potential collateral requirements arising the from credit-risk-related contingent features	$ 52
Georgia Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	4,000,000
Estimated pre-tax losses that will be reclassified from OCI to interest expense for the next 12-month period	$ 4
Fair value of derivative liabilities with contingent features	1
Maximum potential collateral requirements arising the from credit-risk-related contingent features	$ 52
Alabama Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU	50,000,000
Longest Hedge Date	2018
Estimated pre-tax losses that will be reclassified from OCI to interest expense for the next 12-month period	$ 4
Fair value of derivative liabilities with contingent features	16
Maximum potential collateral requirements arising the from credit-risk-related contingent features	$ 52
Gulf Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU	82,000,000
Longest Hedge Date	2020
Fair value of derivative liabilities with contingent features	$ 22
Maximum potential collateral requirements arising the from credit-risk-related contingent features	$ 52
Mississippi Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU	32,000,000
Longest Hedge Date	2018
Estimated pre-tax losses that will be reclassified from OCI to interest expense for the next 12-month period	$ 1
Fair value of derivative liabilities with contingent features	12
Maximum potential collateral requirements arising the from credit-risk-related contingent features	$ 52
Southern Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	1,000,000
Maximum potential collateral requirements arising the from credit-risk-related contingent features	$ 52
Public Utilities, Inventory, Natural Gas [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU	224,000,000
Public Utilities, Inventory, Natural Gas [Member] | Georgia Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU	50,000,000
Longest Hedge Date	2017
Public Utilities, Inventory, Natural Gas [Member] | Southern Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU	10,000,000
Longest Non-Hedge Date	2017
Public Utilities, Inventory, Fuel [Member]
Derivative [Line Items]
Longest Hedge Date	2020
Longest Non-Hedge Date	2017