Note 3 - Regulated Operations (Details) - Estimated Recognition of Rate Making Assets - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Regulatory Assets [Line Items]
Regulatory Asset	$ 690	$ 714	$ 891
Regulatory Asset Off Balance Sheet [Member]
Regulatory Assets [Line Items]
Regulatory Asset	141	127	109
Atlanta Gas Light [Member] | Regulatory Asset Off Balance Sheet [Member]
Regulatory Assets [Line Items]
Regulatory Asset	126	113	96
Virginia Natural Gas [Member] | Regulatory Asset Off Balance Sheet [Member]
Regulatory Assets [Line Items]
Regulatory Asset	11	12	12
Elizabethtown Gas [Member] | Regulatory Asset Off Balance Sheet [Member]
Regulatory Assets [Line Items]
Regulatory Asset	3	$ 2	$ 1
Nicor Gas [Member] | Regulatory Asset Off Balance Sheet [Member]
Regulatory Assets [Line Items]
Regulatory Asset	$ 1