Basis of Presentation (Details) (Alabama Gas Corporation, USD $) In Millions, except Per Share data	3 Months Ended
Mar. 31, 2010
Overstatement to allowance for doubtful accounts
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount	$ 3.0
Overstatement of net income
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount	$ 0.6
Earnings Per Share, Diluted
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Per Share	$ 0.01

Amount of each individual error being corrected in the correcting adjustment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 1
-Section N

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 1.N.Q3)
-URI http://asc.fasb.org/extlink&oid=6369664&loc=d3e30840-122693

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration