SIGNIFICANT ACCOUNTING POLICIES (Government Grants) (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Accounting Policies [Abstract]
Employee retention credit under the CARES Act and the subsidy under CEWS	$ 42.3

Employee Retention Credit Amount, CARES Act And CEWS

No definition available.

Name:	clh_EmployeeRetentionCreditAmountCARESActAndCEWS
Namespace Prefix:	clh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration