Note 5 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Nicor Gas [Member]
Note 5 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
Realized losses related to hedging natural gas costs	$ (18)	$ 10	$ (21)	$ 12
Elizabethtown Gas [Member]
Note 5 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
Realized losses related to hedging natural gas costs	$ (4)	$ 2	$ (8)	$ 5