Income Tax Uncertainties	9 Months Ended
Income Tax Uncertainties	Jun. 30, 2013
Income Tax Disclosure [Abstract]
Income Tax Uncertainties	I. Income Tax Uncertainties Cabot files U.S. federal and state and non-U.S. income tax returns in jurisdictions with varying statutes of limitations. The 2007 through 2012 tax years remain subject to examination by the IRS and various tax years from 2004 through 2012 remain subject to examination by the respective state tax authorities. In significant non-U.S. jurisdictions, various tax years from 2003 through 2012 remain subject to examination by their respective tax authorities. Cabot’s significant non-U.S. jurisdictions include Argentina, Canada, China, France, Germany, Italy, Japan, the Netherlands, and the United Kingdom. Certain Cabot subsidiaries are under audit in jurisdictions outside of the U.S. In addition, certain statutes of limitations are scheduled to expire in the near future. It is reasonably possible that a change in the unrecognized tax benefits may also occur within the next twelve months related to the settlement of one or more of these audits, however, an estimated range of the impact on the unrecognized tax benefits cannot be quantified at this time. During the three and nine months ended June 30, 2013, there were no material changes in the amount of unrecognized tax benefits.

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.

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