Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Schedule of Quantifying Prior Year Misstatement Not Corrected Due to Materiality [Line Items]
Increase (decrease) in operating cash flow due to uncorrected error due to materiality	$ 1.9
Alabama Gas Corporation
Schedule of Quantifying Prior Year Misstatement Not Corrected Due to Materiality [Line Items]
Increase (decrease) in operating cash flow due to uncorrected error due to materiality	$ (0.8)