EARNINGS (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Income from continuing operations									$ 838	$ 736	$ 772
Income from discontinued operations, net of taxes									20	0	0
Net income attributable to Quest Diagnostics	$ 253	$ 215	$ 226	$ 164	$ 127	$ 213	$ 219	$ 177	858	736	772
Less: Earnings allocated to participating securities									3	3	3
Earnings available to Quest Diagnostics’ common stockholders – basic and diluted									$ 835
Earnings available to Quest Diagnostics' common stockholders - basic and diluted										$ 733	$ 769
Weighted average common shares outstanding - basic									134	136	137
Stock options and performance share units									2	3	3
Weighted average common shares outstanding - diluted									136	139	140
Income from continuing operations (in dollars per share)	$ 1.88	$ 1.59	$ 1.52	$ 1.22	$ 0.93	$ 1.56	$ 1.60	$ 1.30	$ 6.21	$ 5.39	$ 5.63
Income from discontinued operations (in dollars per share)	0	0	0.15	0	0	0	0	0	0.15	0	0
Net income (in dollars per share)	1.88	1.59	1.67	1.22	0.93	1.56	1.60	1.30	6.36	5.39	5.63
Income from continuing operations (in dollars per share)	1.86	1.56	1.51	1.20	0.92	1.53	1.57	1.27	6.13	5.29	5.50
Income from discontinued operations (in dollars per share)	0	0	0.15	0	0	0	0	0	0.15	0	0
Net income (in dollars per share)	$ 1.86	$ 1.56	$ 1.66	$ 1.20	$ 0.92	$ 1.53	$ 1.57	$ 1.27	$ 6.28	$ 5.29	$ 5.50
Stock options and performance share units not included due to their antidilutive effect									3	2	2