Document And Entity Information - USD ($)	12 Months Ended
	Jun. 30, 2018	Jul. 31, 2018	Dec. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Entity Public Float			$ 51,688,560,196
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Entity Registrant Name	AUTOMATIC DATA PROCESSING INC
Entity Central Index Key	0000008670
Current Fiscal Year End Date	--06-30
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		438,082,756