BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Percentage of net revenues	100.00%	100.00%
Total net revenues	$ 1,891	$ 1,884
Total operating income	248	272
Non-operating expenses, net	(35)	(43)
Income before income taxes and equity in earnings of equity method investees	213	229
Income tax expense	(50)	(52)
Equity in earnings of equity method investees, net of taxes	13	12
Net income	176	189
Less: Net income attributable to noncontrolling interests	12	12
Net income attributable to Quest Diagnostics	$ 164	$ 177
DIS business
Segment Reporting Information [Line Items]
Percentage of net revenues	96.00%	96.00%
Total net revenues	$ 1,812	$ 1,803
Total operating income	$ 280	$ 308
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	$ 79	$ 81
Total operating income	9	11
General corporate activities
Segment Reporting Information [Line Items]
Total operating income	$ (41)	$ (47)