Note 4 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Nicor Gas [Member]
Note 4 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
RealizedLossesHedgingNaturalGasCosts	$ 9	$ (25)	$ 8	$ (26)
Elizabethtown Gas [Member]
Note 4 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
RealizedLossesHedgingNaturalGasCosts	$ (1)	$ (7)	$ (4)	$ (16)