Note 4 - Derivative Instruments (Details) - Net Long Natural Gas Contracts	Jun. 30, 2013 ft3		Dec. 31, 2012 ft3		Jun. 30, 2012 ft3
Hedge designation
Cash flow hedges	3,000,000,000	[1],[2]	6,000,000,000	[1]	7,000,000,000	[1]
Not designated as hedges	221,000,000,000	[1],[2]	96,000,000,000	[1]	47,000,000,000	[1]
Total hedges	224,000,000,000	[1],[2]	102,000,000,000	[1]	54,000,000,000	[1]
Hedge position
Short position	(2,311,000,000,000)	[1],[2]	(1,955,000,000,000)	[1]	(2,018,000,000,000)	[1]
Long position	2,535,000,000,000	[1],[2]	2,057,000,000,000	[1]	2,072,000,000,000	[1]
Net long position	224,000,000,000	[1],[2]	102,000,000,000	[1]	54,000,000,000	[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 98% of these contracts have durations of two years or less and the remaining 2% expire between 2 and 6 years.