BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Percentage of net revenues	100.00%	100.00%	100.00%	100.00%
Total net revenues	$ 1,889	$ 1,856	$ 5,692	$ 5,537
Total operating income	304	298	881	896
Non-operating expenses, net	(38)	(40)	(122)	(100)
Income before income taxes and equity in earnings of equity method investees	266	258	759	796
Income tax expense	(48)	(92)	(142)	(264)
Equity in earnings of equity method investees, net of taxes	9	9	32	25
Net income	227	175	649	557
Less: Net income attributable to noncontrolling interests	14	14	40	39
Net income attributable to Quest Diagnostics	$ 213	$ 161	$ 609	$ 518
DIS business [Member]
Segment Reporting Information [Line Items]
Percentage of net revenues	96.00%	96.00%	96.00%	95.40%
Total net revenues	$ 1,810	$ 1,777	$ 5,448	$ 5,283
Total operating income	333	334	982	987
All other operating segments [Member]
Segment Reporting Information [Line Items]
Total net revenues	79	79	244	254
Total operating income	11	10	33	40
General corporate activities [Member]
Segment Reporting Information [Line Items]
Total operating income	$ (40)	$ (46)	$ (134)	$ (131)