| **INCOME TAXES**            | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **INCOME TAXES [Abstract]** | Â                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| INCOME TAXES [Text Block]   | 6.INCOME TAXESThe effective income tax rate for the three months ended June 30, 2011 increased to 36.5 percent from 34.2 percent in the prior year.  The higher effective income tax rate for the three months ended June 30, 2011 is due primarily to lower forecasted annual untaxed foreign shipping earnings and an increase to the Illinois state income tax rate, partially offset by lower forecasted annual pretax income (which causes a lower effective income tax rate since permanent differences and tax credits are a larger share of pretax income).  The effective income tax rate for the six months ended June 30, 2011 decreased to 31.4 percent from 32.6 percent in the prior year.  The lower effective income tax rate for the six months ended June 30, 2011 is due to an adjustment to reduce certain state income tax liabilities in the first quarter of 2011 and lower forecasted annual pretax income, partially offset by lower forecasted annual untaxed foreign shipping earnings and an increase to the Illinois state income tax rate.  Effective January 1, 2011, the State of Illinois raised the corporate income tax rate from 7.3 percent to 9.5 percent.In 2006, the company reorganized certain shipping and related operations.  The reorganization allows the company to take advantage of certain provisions of the Jobs Act that provide the opportunity for tax savings subsequent to the date of the reorganization.  Generally, to the extent foreign shipping earnings are not repatriated to the United States, such earnings are not expected to be subject to current taxation.  In addition, to the extent such earnings are determined to be indefinitely reinvested offshore, no deferred income tax expense would be recorded by the company.  For the three months ended June 30, 2011 and 2010, an income tax benefit (expense) has not been recognized (provided) on approximately $4 million and $(2) million, respectively, of foreign company shipping losses (earnings).  For the six months ended June 30, 2011 and 2010, an income tax benefit has not been recognized on approximately $8 million and $1 million, respectively, of foreign company shipping losses.  As of June 30, 2011, Nicor has not recorded deferred income taxes of approximately $57 million on approximately $162 million of cumulative undistributed foreign earnings.The company's major tax jurisdictions include the United States and Illinois, with tax returns examined by the IRS and IDR, respectively.  At June 30, 2011, the years that remain subject to examination include years beginning after 2006 for the IRS and the IDR.  The company had no liability for unrecognized tax benefits at June 30, 2011.  The decrease in the liability for unrecognized tax benefits from $2.9 million at December 31, 2010 was due to a reduction in state tax reserves.  The company does not believe that it is reasonably possible that a significant change in the liability for unrecognized tax benefits could occur within 12 months.The balance of unamortized investment tax credits at June 30, 2011, December 31, 2010 and June 30, 2010 was $23.4 million, $24.3 million and $24.2 million, respectively. |

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| - Definition
The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.
+ References
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