Note 5 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Nicor Gas [Member]
Note 5 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
Realized losses related to hedging natural gas costs	$ 2	$ (1)
Elizabethtown Gas [Member]
Note 5 - Derivative Instruments (Details) - Gains and Losses on Derivative Instruments [Line Items]
Realized losses related to hedging natural gas costs	$ 3	$ (3)