Note 5 - Derivative Instruments (Detail) - Net Long Natural Gas Contracts	Dec. 31, 2012 ft3		Dec. 31, 2011 ft3
Hedge designation:
Cash flow hedges	6,000,000,000	[1],[2]	5,000,000,000	[1]
Not designated as hedges	96,000,000,000	[1],[2]	186,000,000,000	[1]
Total hedges	102,000,000,000	[1],[2]	191,000,000,000	[1]
Hedge position:
Short position	(1,955,000,000,000)	[1],[2]	(1,680,000,000,000)	[1]
Long position	2,057,000,000,000	[1],[2]	1,871,000,000,000	[1]
Net long position	102,000,000,000	[1],[2]	191,000,000,000	[1]

[1] Volumes related to Nicor Gas exclude variable-priced contracts, which are accounted for as derivatives, but whose fair values are not directly impacted by changes in commodity prices.

[2] Approximately 99% of these contracts have durations of two years or less and the remaining 1% expire in 3 to 6 years.