Income Taxes	3 Months Ended
Jan. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES On December 22, 2017, the Tax Cuts and Jobs Act (the "Tax Act") was enacted. The Tax Act significantly revises the U.S. corporate income tax by, among other things, lowering the statutory corporate income tax rate (“federal tax rate”) from 35% to 21% effective January 1, 2018, implementing a modified territorial tax system, and imposing a mandatory one-time transition tax on accumulated earnings of foreign subsidiaries. The enactment of the Tax Act resulted in Ciena recording a provisional tax expense of $472.8 million in fiscal 2018. In the first quarter of fiscal 2019, the measurement period under the Tax Act concluded, which resulted in immaterial adjustments to our provisional estimates. In addition, the realizability of U.S. tax carryforwards is not impacted by the base erosion and anti-abuse tax (BEAT), and the BEAT is a period cost when incurred. The effective tax rate for the three months ended January 31, 2019 was lower than the effective tax rate for the three months ended January 31, 2018, primarily due to the impact of the Tax Act which reduced the U.S. federal corporate income tax rate from 35% to 21% effective January 1, 2018. The reduction of the U.S. federal corporate income tax rate during the three months ended January 31, 2018, required the remeasurement of the net deferred tax assets and liabilities (“DTA”). Also, Ciena recorded U.S. transition tax in the three months ended January 31, 2018.

INCOME TAXES

On December 22, 2017, the Tax Cuts and Jobs Act (the "Tax Act") was enacted. The Tax Act significantly revises the U.S. corporate income tax by, among other things, lowering the statutory corporate income tax rate (“federal tax rate”) from 35% to 21% effective January 1, 2018, implementing a modified territorial tax system, and imposing a mandatory one-time transition tax on accumulated earnings of foreign subsidiaries. The enactment of the Tax Act resulted in Ciena recording a provisional tax expense of $472.8 million in fiscal 2018. In the first quarter of fiscal 2019, the measurement period under the Tax Act concluded, which resulted in immaterial adjustments to our provisional estimates. In addition, the realizability of U.S. tax carryforwards is not impacted by the base erosion and anti-abuse tax (BEAT), and the BEAT is a period cost when incurred.

The effective tax rate for the three months ended January 31, 2019 was lower than the effective tax rate for the three months ended January 31, 2018, primarily due to the impact of the Tax Act which reduced the U.S. federal corporate income tax rate from 35% to 21% effective January 1, 2018. The reduction of the U.S. federal corporate income tax rate during the three months ended January 31, 2018, required the remeasurement of the net deferred tax assets and liabilities (“DTA”). Also, Ciena recorded U.S. transition tax in the three months ended January 31, 2018.