EARNINGS (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share, Basic and Diluted [Abstract]
Income from continuing operations									$ 1,431	$ 838	$ 736
Income from discontinued operations, net of taxes									0	20	0
Net income attributable to Quest Diagnostics	$ 579	$ 568	$ 185	$ 99	$ 253	$ 215	$ 226	$ 164	1,431	858	736
Less: Earnings allocated to participating securities									6	3	3
Earnings available to Quest Diagnostics’ common stockholders – basic and diluted									$ 1,425	$ 835	$ 733
Weighted average common shares outstanding - basic									134	134	136
Stock options and performance share units									2	2	3
Weighted average common shares outstanding - diluted									136	136	139
Income from continuing operations (in dollars per share)	$ 4.28	$ 4.20	$ 1.38	$ 0.74	$ 1.88	$ 1.59	$ 1.52	$ 1.22	$ 10.62	$ 6.21	$ 5.39
Income from discontinued operations (in dollars per share)	0	0	0	0	0	0	0.15	0	0	0.15	0
Net income (in dollars per share)	4.28	4.20	1.38	0.74	1.88	1.59	1.67	1.22	10.62	6.36	5.39
Income from continuing operations (in dollars per share)	4.21	4.14	1.36	0.73	1.86	1.56	1.51	1.20	10.47	6.13	5.29
Income from discontinued operations (in dollars per share)	0	0	0	0	0	0	0.15	0	0	0.15	0
Net income (in dollars per share)	$ 4.21	$ 4.14	$ 1.36	$ 0.73	$ 1.86	$ 1.56	$ 1.66	$ 1.20	$ 10.47	$ 6.28	$ 5.29
Stock options and performance share units not included due to their antidilutive effect									1	3	2