PROPOSED MERGER WITH AGL RESOURCES (Details) (USD $) In Millions, except Share data	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011
PROPOSED MERGER WITH AGL RESOURCES [Abstract]
Cash consideration into which each outstanding share of Nicor's stock will be converted in business merger (dollars per share)	$ 21.20	$ 21.20
Number of shares of AGL Resources' common stock to be received for each share of Nicor common stock in accordance with the merger agreement (shares per share)	0.8382	0.8382
Merger related costs incurred and expensed	$ 0.4	$ 2.8