Note 4 - Derivative Instruments (Detail) - Net Long Natural Gas Contracts	Mar. 31, 2013 ft3		Dec. 31, 2012 ft3		Mar. 31, 2012 ft3
Hedge designation
Cash flow hedges	6,000,000,000	[1],[2]	6,000,000,000	[1],[2]	7,000,000,000	[1],[2]
Not designated as hedges	304,000,000,000	[1],[2]	96,000,000,000	[1],[2]	116,000,000,000	[1],[2]
Total hedges	310,000,000,000	[1],[2]	102,000,000,000	[1],[2]	123,000,000,000	[1],[2]
Hedge position
Short position	(1,902,000,000,000)	[1],[2]	(1,955,000,000,000)	[1],[2]	(1,942,000,000,000)	[1],[2]
Long position	2,212,000,000,000	[1],[2]	2,057,000,000,000	[1],[2]	2,065,000,000,000	[1],[2]
Net long position	310,000,000,000	[1],[2]	102,000,000,000	[1],[2]	123,000,000,000	[1],[2]

[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 98% of these contracts have durations of two years or less and the remaining 2% expire between 2 and 6 years.