Significant Accounting Policies - Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2017	Oct. 01, 2016
Accounting Policies [Abstract]
Unremitted earnings of foreign subsidiaries not yet provided tax	$ 1,150	$ 574

Unremitted Earnings of Foreign Subsidiaries not yet provided tax

No definition available.

Name:	cohr_UnremittedEarningsofForeignSubsidiariesnotyetprovidedtax
Namespace Prefix:	cohr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration