Note 4 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Nicor Gas [Member]
Note 4 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
Realized losses related to hedging natural gas costs	$ (6)	$ (12)	$ 2	$ (60)
Elizabethtown Gas [Member]
Note 4 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
Realized losses related to hedging natural gas costs	$ (1)	$ (6)	$ (5)	$ (23)