Commitments and Contingencies (Details) - Commitments and Agreements (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Jun. 30, 2010
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation, Time Period	March 2012
Alabama Gas Corporation | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Time Period	August 2020
Long-term Purchase Commitment, Minimum Quantity Required	222
Recorded Unconditional Purchase Obligation	$ 2.0	$ 2.0
Recorded Unconditional Purchase Obligation, Market Value	2.0	2.0
Alabama Gas Corporation | Natural Gas, Delivery and Storage [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	126
Long-term Purchase Commitment, Time Period	September 2024
Long Term Commitments Expense Recognized in Statements of Operations		$ 25.8	$ 26.8