EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Amounts attributable to Quest Diagnostics’ common stockholders:
Income from continuing operations	$ 568	$ 215	$ 852	$ 585
Income from discontinued operations, net of taxes	0	0	0	20
Net income attributable to Quest Diagnostics	568	215	852	605
Less: Earnings allocated to participating securities	2	1	3	2
Earnings available to Quest Diagnostics’ common stockholders – basic and diluted	$ 566	$ 214	$ 849	$ 583
Weighted average common shares outstanding - basic	135	135	134	135
Stock options and performance share units	2	2	2	1
Weighted average common shares outstanding - diluted	137	137	136	136
Earnings per share attributable to Quest Diagnostics’ common stockholders - basic:
Income from continuing operations (in dollars per share)	$ 4.20	$ 1.59	$ 6.33	$ 4.33
Income from discontinued operations (in dollars per share)	0	0	0	0.15
Net income (in dollars per share)	4.20	1.59	6.33	4.48
Earnings per share attributable to Quest Diagnostics’ common stockholders - diluted:
Income from continuing operations (in dollars per share)	4.14	1.56	6.25	4.27
Income from discontinued operations (in dollars per share)	0	0	0	0.15
Net income (in dollars per share)	$ 4.14	$ 1.56	$ 6.25	$ 4.42
Stock options	1	2	1	3