Income Taxes (Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	$ 12,555,000	$ 10,593,000	$ 24,590,000
Additions based on tax positions related to the current year	4,546,000	3,731,000	3,644,000
Additions for tax positions of prior years	366,000	269,000	2,324,000
Reductions for tax positions of prior years (lapse of statute of limitations)			(39,000)
Reductions for tax positions of prior years	(46,000)	(446,000)
Lapse of statute of limitations	(1,435,000)	(1,592,000)	(1,482,000)
Settlements			(18,444,000)
Unrecognized Tax Benefits, Ending Balance	15,986,000	12,555,000	10,593,000
Gross addition (reduction)			(5,900,000)
Unrecognized income tax benefit liability, additions (release)	(6,900,000)		2,900,000
Income tax interest expense (income) (net of tax benefit) and penalties expense (income)	(15,000)	(25,000)	(1,400,000)
Accrued interest (net of tax benefit) and penalties payments	200,000	200,000
IRS
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Settlements			(1,500,000)
Alabama Gas Corporation
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	307,000	102,000	18,941,000
Additions based on tax positions related to the current year		62,000	13,000
Additions for tax positions of prior years		201,000	1,000
Reductions for tax positions of prior years (lapse of statute of limitations)	(31,000)	(58,000)	(409,000)
Settlements			(18,444,000)
Unrecognized Tax Benefits, Ending Balance	276,000	307,000	102,000
Income tax interest expense (income) (net of tax benefit) and penalties expense (income)	4,000	0	1,400,000
Accrued interest (net of tax benefit) and penalties payments	$ 8,000	$ 4,000