EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Net income attributable to Quest Diagnostics	$ 177	$ 164
Less: Earnings allocated to participating securities	1	1
Earnings available to Quest Diagnostics' common stockholders - basic and diluted	$ 176	$ 163
Weighted average common shares outstanding - basic	136	137
Stock options and performance share units	3	4
Weighted average common shares outstanding - diluted	139	141
Basic (per share)	$ 1.30	$ 1.19
Diluted (per share)	$ 1.27	$ 1.16
Stock options and performance share units not included due to their antidilutive effect	2	1