Employee Benefit Plans - Schedule of Combined Funded Status and Net Periodic Pension Cost and Postretirement Benefit - Postretirement Benefits (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Benefits Plan [Member]
Accumulated other comprehensive loss, tax	$ 9.9	$ 9.9

Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Tax

No definition available.

Name:	cday_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansTax
Namespace Prefix:	cday_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant