Income Tax Uncertainties	6 Months Ended
Income Tax Uncertainties	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Tax Uncertainties	J. 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 2011 through 2014 tax years remain subject to examination by the United States Internal Revenue Service (“IRS”) and various tax years from 2005 through 2014 remain subject to examination by the respective state tax authorities. In significant non-U.S. jurisdictions, various tax years from 2004 through 2014 remain subject to examination by their respective tax authorities. Cabot’s significant non-U.S. jurisdictions include China, France, Germany, Italy, Japan, and the Netherlands. 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 six months ended March 31, 2015, Cabot released uncertain tax positions of $1 million and $12 million, respectively, due to the expirations of statutes of limitations in various jurisdictions. As of October 1, 2014, Cabot adopted a new accounting standard which requires, unless certain conditions exist, an unrecognized tax benefit or a portion of an unrecognized tax benefit be presented in the consolidated financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, similar to a tax loss or a tax credit carryforward. This resulted in a reduction of the liability for uncertain tax positions and deferred tax assets of $5 million.

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+ Details