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DOCUMENT AND ENTITY INFORMATION - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2018
Jan. 31, 2019
Jun. 30, 2018
Document and Entity Information [Abstract]      
Document type 10-K    
Amendment flag false    
Document period end date Dec. 31, 2018    
Document fiscal year focus 2018    
Document fiscal period focus FY    
Entity registrant name QUEST DIAGNOSTICS INC    
Entity central index key 0001022079    
Current fiscal year end date --12-31    
Entity filer category Large Accelerated Filer    
Entity public float     $ 14.9
Entity common stock, shares outstanding   134,261,768  
Entity current reporting status Yes    
Entity voluntary filers No    
Entity well-known seasoned issuer Yes