EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share, Basic and Diluted [Abstract]
Net income attributable to Quest Diagnostics	$ 164	$ 177
Less: Earnings allocated to participating securities	1	1
Earnings available to Quest Diagnostics' common stockholders - basic and diluted	$ 163	$ 176
Weighted average common shares outstanding - basic	134	136
Stock options and performance share units	2	3
Weighted average common shares outstanding - diluted	136	139
Basic (per share)	$ 1.22	$ 1.30
Diluted (per share)	$ 1.20	$ 1.27
Stock options and performance share units not included due to their antidilutive effect	4	2