BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Percentage of net revenues	100.00%	100.00%
Total net revenues	$ 1,822	$ 1,891
Total operating income	175	248
Non-operating expenses, net	(57)	(35)
Income before income taxes and equity in earnings of equity method investees	118	213
Income tax expense	(26)	(50)
Equity in earnings of equity method investees, net of taxes	14	13
Net income	106	176
Less: Net income attributable to noncontrolling interests	7	12
Net income attributable to Quest Diagnostics	$ 99	$ 164
DIS business
Segment Reporting Information [Line Items]
Percentage of net revenues	96.00%	96.00%
Total net revenues	$ 1,744	$ 1,812
Total operating income	$ 205	$ 280
DIS business | Minimum
Segment Reporting Information [Line Items]
Percentage of net revenues	95.00%	95.00%
All other operating segments
Segment Reporting Information [Line Items]
Total net revenues	$ 78	$ 79
Total operating income	9	9
General corporate activities
Segment Reporting Information [Line Items]
Total operating income	$ (39)	$ (41)