Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Schedule of Quantifying Prior Year Misstatement Not Corrected Due to Materiality [Line Items]
Decrease in operating cash flow due to uncorrected error due to materiality	$ 3.9
Alabama Gas Corporation
Schedule of Quantifying Prior Year Misstatement Not Corrected Due to Materiality [Line Items]
Decrease in operating cash flow due to uncorrected error due to materiality	$ 4.5