Derivatives - Narrative (Details) BTU in Millions, $ in Millions	3 Months Ended
Mar. 31, 2016 USD ($) BTU
Derivative [Line Items]
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features \| $	$ 49
Southern Company [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints \| BTU	4

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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