Cover Page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 16, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-12215
Entity Registrant Name	QUEST DIAGNOSTICS INC
Entity Central Index Key	0001022079
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	16-1387862
Entity Address, Address Line One	500 Plaza Drive
Entity Address, City or Town	Secaucus,
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07094
City Area Code	(973)
Local Phone Number	520-2700
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	DGX
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		134,697,086