BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Percentage of net revenues	100.00%	100.00%	100.00%	100.00%
Total net revenues	$ 2,550	$ 1,827	$ 5,270	$ 3,649
Total operating income	533	283	1,193	458
Non-operating income (expense), net	284	(28)	250	(85)
Income before income taxes and equity in earnings of equity method investees	817	255	1,443	373
Income tax expense	(177)	(66)	(330)	(92)
Equity in earnings of equity method investees, net of taxes	10	4	27	18
Net income	650	193	1,140	299
Less: Net income attributable to noncontrolling interests	19	8	40	15
Net income attributable to Quest Diagnostics	631	185	1,100	284
Routine clinical testing services
Segment Reporting Information [Line Items]
Total net revenues	1,150	812	2,182	1,757
COVID-19 Testing Services
Segment Reporting Information [Line Items]
Total net revenues	511	582	1,339	606
Gene-based and esoteric testing services
Segment Reporting Information [Line Items]
Total net revenues	673	294	1,326	935
Anatomic pathology testing services
Segment Reporting Information [Line Items]
Total net revenues	140	76	270	210
All other services
Segment Reporting Information [Line Items]
Total net revenues	$ 76	$ 63	$ 153	$ 141
DIS business
Segment Reporting Information [Line Items]
Percentage of net revenues	97.00%	97.00%	97.00%	96.00%
Total net revenues	$ 2,474	$ 1,764	$ 5,117	$ 3,508
Total operating income	$ 601	$ 280	$ 1,313	$ 485
DIS business | Minimum
Segment Reporting Information [Line Items]
Percentage of net revenues	95.00%	95.00%	95.00%	95.00%
All other operating segments
Segment Reporting Information [Line Items]
Total net revenues	$ 76	$ 63	$ 153	$ 141
Total operating income	9	4	18	13
General corporate activities
Segment Reporting Information [Line Items]
Total operating income	$ (77)	$ (1)	$ (138)	$ (40)