Reclassifications of Accumulated Other Comprehensive Income (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Pension and Postretirement Plans Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Pension and Postretirement Plans Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Pension and Postretirement Plans Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Pension and Postretirement Plans Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Commodity contracts Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Commodity contracts Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Commodity contracts Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Commodity contracts Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Interest rate swap Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Interest rate swap Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2014 Interest rate swap Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Jun. 30, 2013 Interest rate swap Cash Flow Hedges Reclassification out of Accumulated Other Comprehensive Income	Mar. 31, 2014 Supplemental Employee Retirement Plan	Mar. 31, 2013 Supplemental Employee Retirement Plan	Mar. 31, 2013 Supplemental Employee Retirement Plan Alabama Gas Corporation
Gains (losses) on cash flow hedges:
Reclassification Adjustment from AOCI on Derivatives																	$ 5,735,000	$ 4,503,000	$ 9,789,000	$ 21,792,000	$ (1,588,000)	$ (426,000)	$ (2,033,000)	$ (836,000)
Total									4,147,000	4,077,000	7,756,000	20,956,000	(1,732,000)	(2,249,000)	(10,369,000)	(5,029,000)
Income tax expense	1,016,000	(46,229,000)	(7,232,000)	(50,273,000)					(1,623,000)	(1,562,000)	(3,008,000)	(7,989,000)	606,000	788,000	3,630,000	1,761,000
Net of tax					1,398,000	1,054,000	(1,991,000)	9,699,000	2,524,000	2,515,000	4,748,000	12,967,000	(1,126,000)	(1,461,000)	(6,739,000)	(3,268,000)
Pension and postretirement plans:
Transition obligation													(9,000)	(74,000)	(19,000)	(147,000)
Prior service cost													(74,000)	(78,000)	(148,000)	(157,000)
Actuarial losses													(1,289,000)	(2,097,000)	(2,580,000)	(4,350,000)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss) on Settlement Charges, Operation, before Tax															(7,622,000)	0
Actuarial losses on settlement charges													(360,000)	0	0	(375,000)
Settlement charges																									400,000	500,000
Settlement charges expensed																										100,000
Settlements recognized as a pension asset																											$ 400,000