Commitments and Contingencies	6 Months Ended
Apr. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Canadian Grant During the second quarter of fiscal 2018, Ciena entered into agreements related to the Evolution of Networking Services through a Corridor in Quebec and Ontario for Research and Innovation ("ENCQOR") project with the Canadian federal government, the government of the province of Ontario and the government of the province of Quebec to develop a 5G technology corridor between Quebec and Ontario to promote research and development, small business enterprises and entrepreneurs in Canada. Under these agreements, Ciena can receive up to an aggregate CAD$57.6 million (approximately $45.0 million) in reimbursement by the three Canadian government entities for eligible costs over a period commencing on February 20, 2017 and ending on March 31, 2022. Ciena anticipates receiving recurring disbursements over this period. Amounts received under the agreements are subject to recoupment in the event that Ciena fails to achieve certain minimum investment, employment and project milestones. During the second quarter of fiscal 2018, Ciena recorded a CAD$10.3 million (approximately $8.1 million) benefit as a reduction in research and development expense, related to eligible costs that it incurred from the commencement date of February 20, 2017 to April 30, 2018, because it believes it has complied with the conditions of the agreements entitling it to this amount. In future periods, through the term of these agreements, Ciena expects to record a quarterly benefit to operating expense of approximately CAD$2.95 million (approximately $2.3 million) related to these grants. Foreign Tax Contingencies Ciena is subject to various tax liabilities arising in the ordinary course of business. Ciena does not expect that the ultimate settlement of these tax liabilities will have a material effect on its results of operations, financial position or cash flows. Litigation As a result of the acquisition of Cyan in August 2015, Ciena became a defendant in a securities class action lawsuit. On April 1, 2014, a purported stockholder class action lawsuit was filed in the Superior Court of California, County of San Francisco, against Cyan, the members of Cyan’s board of directors, Cyan’s former Chief Financial Officer, and the underwriters of Cyan’s initial public offering. On April 30, 2014, a substantially similar lawsuit was filed in the same court against the same defendants. The two cases were consolidated as Beaver County Employees Retirement Fund, et al. v. Cyan, Inc. et al., Case No. CGC-14-538355. The consolidated complaint alleges violations of federal securities laws on behalf of a purported class consisting of purchasers of Cyan’s common stock pursuant or traceable to the registration statement and prospectus for Cyan’s initial public offering in April 2013, and seeks unspecified compensatory damages and other relief. On May 19, 2015, the proposed class was certified. On August 25, 2015, the defendants filed a motion for judgment on the pleadings based on an alleged lack of subject matter jurisdiction over the case, which motion was denied on October 23, 2015. On May 24, 2016, the defendants filed a petition for a writ of certiorari on the jurisdiction issue with the U.S. Supreme Court, which petition was granted on June 27, 2017. The matter was stayed by the Superior Court pending the outcome of the Supreme Court’s decision. On March 20, 2018, the Supreme Court held that the Superior Court had subject matter jurisdiction over the case. A case management conference is scheduled before the Superior Court during the third quarter of fiscal 2018. Ciena believes that the consolidated lawsuit is without merit and intends to defend it vigorously. Internal Investigations During fiscal 2017, one of Ciena’s third-party vendors raised allegations about certain questionable payments to one or more individuals employed by a customer in a country in the ASEAN region. Ciena promptly initiated an internal investigation into the matter, with the assistance of outside counsel, which investigation corroborated direct and indirect payments to one such individual and sought to determine whether the payments may have violated applicable laws and regulations, including the U.S. Foreign Corrupt Practices Act (“FCPA”). In September 2017, Ciena voluntarily contacted the SEC and the U.S. Department of Justice (“DOJ”) to advise them of the relevant events and the findings of Ciena’s internal investigation. With the direct oversight of Ciena's Board of Directors, Ciena continues to cooperate fully with the SEC and DOJ in their review of the investigation. Ciena’s operations in the relevant country have constituted less than 1.5% of consolidated revenues as reported by Ciena in each fiscal year since 2012. Ciena does not currently anticipate that this matter will have a material adverse effect on its business, financial condition or results of operations. However, as discussions with the SEC and DOJ are ongoing, the ultimate outcome of this matter cannot be predicted at this time. As of the filing of this Report, no provision with respect to this matter has been made in Ciena’s consolidated financial statements. Any determination that Ciena’s operations or activities are not in compliance with the FCPA or other applicable laws or regulations could result in the imposition of fines, civil and criminal penalties, and equitable remedies, including disgorgement or injunctive relief. In addition to the matters described in “Litigation” and “Internal Investigations” above, Ciena is subject to various legal proceedings, claims and other matters arising in the ordinary course of business, including those that relate to employment, commercial, tax and other regulatory matters. Ciena is also subject to intellectual property related claims, including claims against third parties that may involve contractual indemnification obligations on the part of Ciena. Ciena does not expect that the ultimate costs to resolve such matters will have a material effect on its results of operations, financial position or cash flows.

COMMITMENTS AND CONTINGENCIES

Canadian Grant

During the second quarter of fiscal 2018, Ciena entered into agreements related to the Evolution of Networking Services through a Corridor in Quebec and Ontario for Research and Innovation ("ENCQOR") project with the Canadian federal government, the government of the province of Ontario and the government of the province of Quebec to develop a 5G technology corridor between Quebec and Ontario to promote research and development, small business enterprises and entrepreneurs in Canada. Under these agreements, Ciena can receive up to an aggregate CAD$57.6 million (approximately $45.0 million) in reimbursement by the three Canadian government entities for eligible costs over a period commencing on February 20, 2017 and ending on March 31, 2022. Ciena anticipates receiving recurring disbursements over this period. Amounts received under the agreements are subject to recoupment in the event that Ciena fails to achieve certain minimum investment, employment and project milestones. During the second quarter of fiscal 2018, Ciena recorded a CAD$10.3 million (approximately $8.1 million) benefit as a reduction in research and development expense, related to eligible costs that it incurred from the commencement date of February 20, 2017 to April 30, 2018, because it believes it has complied with the conditions of the agreements entitling it to this amount. In future periods, through the term of these agreements, Ciena expects to record a quarterly benefit to operating expense of approximately CAD$2.95 million (approximately $2.3 million) related to these grants.

Foreign Tax Contingencies

Ciena is subject to various tax liabilities arising in the ordinary course of business. Ciena does not expect that the ultimate settlement of these tax liabilities will have a material effect on its results of operations, financial position or cash flows.

Litigation

As a result of the acquisition of Cyan in August 2015, Ciena became a defendant in a securities class action lawsuit. On April 1, 2014, a purported stockholder class action lawsuit was filed in the Superior Court of California, County of San Francisco, against Cyan, the members of Cyan’s board of directors, Cyan’s former Chief Financial Officer, and the underwriters of Cyan’s initial public offering. On April 30, 2014, a substantially similar lawsuit was filed in the same court against the same defendants. The two cases were consolidated as Beaver County Employees Retirement Fund, et al. v. Cyan, Inc. et al., Case No. CGC-14-538355. The consolidated complaint alleges violations of federal securities laws on behalf of a purported class consisting of purchasers of Cyan’s common stock pursuant or traceable to the registration statement and prospectus for Cyan’s initial public offering in April 2013, and seeks unspecified compensatory damages and other relief. On May 19, 2015, the proposed class was certified. On August 25, 2015, the defendants filed a motion for judgment on the pleadings based on an alleged lack of subject matter jurisdiction over the case, which motion was denied on October 23, 2015. On May 24, 2016, the defendants filed a petition for a writ of certiorari on the jurisdiction issue with the U.S. Supreme Court, which petition was granted on June 27, 2017. The matter was stayed by the Superior Court pending the outcome of the Supreme Court’s decision. On March 20, 2018, the Supreme Court held that the Superior Court had subject matter jurisdiction over the case. A case management conference is scheduled before the Superior Court during the third quarter of fiscal 2018. Ciena believes that the consolidated lawsuit is without merit and intends to defend it vigorously.

Internal Investigations

During fiscal 2017, one of Ciena’s third-party vendors raised allegations about certain questionable payments to one or more individuals employed by a customer in a country in the ASEAN region. Ciena promptly initiated an internal investigation into the matter, with the assistance of outside counsel, which investigation corroborated direct and indirect payments to one such individual and sought to determine whether the payments may have violated applicable laws and regulations, including the U.S. Foreign Corrupt Practices Act (“FCPA”). In September 2017, Ciena voluntarily contacted the SEC and the U.S. Department of Justice (“DOJ”) to advise them of the relevant events and the findings of Ciena’s internal investigation. With the direct oversight of Ciena's Board of Directors, Ciena continues to cooperate fully with the SEC and DOJ in their review of the investigation.

Ciena’s operations in the relevant country have constituted less than 1.5% of consolidated revenues as reported by Ciena in each fiscal year since 2012. Ciena does not currently anticipate that this matter will have a material adverse effect on its business, financial condition or results of operations. However, as discussions with the SEC and DOJ are ongoing, the ultimate outcome of this matter cannot be predicted at this time. As of the filing of this Report, no provision with respect to this matter has been made in Ciena’s consolidated financial statements. Any determination that Ciena’s operations or activities are not in compliance with the FCPA or other applicable laws or regulations could result in the imposition of fines, civil and criminal penalties, and equitable remedies, including disgorgement or injunctive relief.

In addition to the matters described in “Litigation” and “Internal Investigations” above, Ciena is subject to various legal proceedings, claims and other matters arising in the ordinary course of business, including those that relate to employment, commercial, tax and other regulatory matters. Ciena is also subject to intellectual property related claims, including claims against third parties that may involve contractual indemnification obligations on the part of Ciena. Ciena does not expect that the ultimate costs to resolve such matters will have a material effect on its results of operations, financial position or cash flows.