| **GUARANTEES AND INDEMNITIES**            | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **GUARANTEES AND INDEMNITIES [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| GUARANTEES AND INDEMNITIES [Text Block]   | 14.GUARANTEES AND INDEMNITIES Nicor and certain subsidiaries enter into various financial and performance guarantees and indemnities providing assurance to third parties. Financial guarantees.  TEL has an obligation to restore to zero any deficit in its equity account for income tax purposes in the unlikely event that Triton is liquidated and a deficit balance remains.  This obligation continues for the life of the Triton partnerships and any payment is effectively limited to the assets of TEL, which were zero at September 30, 2011.  Nicor believes the likelihood of any such payment by TEL is remote.  No liability has been recorded for this obligation. Performance guarantees.  Directly or through a subsidiary, Nicor Services markets product warranty contracts that provide for the repair of heating, ventilation and air conditioning equipment, natural gas lines and other appliances within homes.  Revenues from these product warranty contracts are recognized ratably over the coverage period, and related repair costs are charged to expense as incurred.  Repair expenses of $3.2 million and $9.1 million were incurred in the three and nine months ended September 30, 2011, respectively, and $2.7 million and $7.5 million, respectively, for the same periods in 2010. Indemnities.  In certain instances, Nicor has undertaken to indemnify current property owners and others against costs associated with the effects and/or remediation of contaminated sites for which the company may be responsible under applicable federal or state environmental laws, generally with no limitation as to the amount.  These indemnifications relate primarily to ongoing coal tar cleanup, as discussed in Note 15 – Contingencies – Manufactured Gas Plant Sites.  Nicor believes that the likelihood of payment under its other environmental indemnifications is remote.  No liability has been recorded for such indemnifications. Nicor has also indemnified, to the fullest extent permitted under the laws of the State of Illinois and any other applicable laws, its present and former directors, officers and employees against expenses they may incur in connection with litigation they are a party to by reason of their association with the company.  There is generally no limitation as to the amount.  During 2007, the SEC filed a civil injunctive action against three former officers of Nicor relating to the PBR Plan.  Defense costs that are being incurred by these former officers in connection with the SEC action currently are being tendered to, and paid by, the company’s insurer.  In July 2010, one of these former officers settled the SEC’s action against him and was indemnified by Nicor.  While the company does not expect to incur significant costs relating to the indemnification of present and former directors, officers and employees after taking into account available insurance, it is not possible to estimate the maximum future potential payments. |

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| - Definition
Provides pertinent information about each guarantee obligation, or each group of similar guarantee obligations, including (a) the nature of the guarantee, including its term, how it arose, and the events or circumstances that would require the guarantor to perform under the guarantee; (b) the maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee; (c) the current carrying amount of the liability, if any, for the guarantor's obligations under the guarantee; and (d) the nature of any recourse provisions under the guarantee, and any assets held either as collateral or by third parties, and any relevant related party disclosure. An agreement (contract) that contingently requires the guarantor to make payments to the guaranteed party in compensation for that party's or parties' loss or injury attributable to specified events or actions, such as a patent infringement action against an entity that relied on certain representations as to ownership rights made by a software vendor.
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