Note 5 - Derivative Instruments (Details) - Net Long Natural Gas Contracts	Dec. 31, 2014 ft3		Dec. 31, 2013 ft3
Note 5 - Derivative Instruments (Details) - Net Long Natural Gas Contracts [Line Items]
Cash flow hedges	9,000,000,000	[1],[2]	6,000,000,000	[1]
Not designated as hedges	75,000,000,000	[1],[2]	183,000,000,000	[1]
Total volumes	84,000,000,000	[1],[2]	189,000,000,000	[1]
Net long position	84,000,000,000	[1],[2]	189,000,000,000	[1]
Designated as Hedging Instrument [Member]
Note 5 - Derivative Instruments (Details) - Net Long Natural Gas Contracts [Line Items]
Short position	(4,000,000,000)	[1],[2]	(6,000,000,000)	[1]
Long position	16,000,000,000	[1],[2]	12,000,000,000	[1]
Not Designated as Hedging Instrument [Member]
Note 5 - Derivative Instruments (Details) - Net Long Natural Gas Contracts [Line Items]
Short position	(2,828,000,000,000)	[1],[2]	(2,616,000,000,000)	[1]
Long position	2,900,000,000,000	[1],[2]	2,799,000,000,000	[1]

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

[2] Approximately 100% of these contracts have durations of two years or less and less than 1% expire between two and five years.