BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Percentage of net revenues from the DIS business									100.00%	100.00%	100.00%
Total net revenues	$ 1,926	$ 1,956	$ 1,953	$ 1,891	$ 1,839	$ 1,889	$ 1,919	$ 1,884	$ 7,726	$ 7,531	$ 7,402
Total operating income									1,231	1,101	1,165
Non-operating expenses, net									(155)	(175)	(135)
Income from continuing operations before income taxes and equity in earnings of equity method investees									1,076	926	1,030
Income tax expense									(247)	(182)	(241)
Equity in earnings of equity method investees, net of taxes									57	44	35
Income from continuing operations	265	226	219	176	139	227	233	189	886	788	824
Income (loss) from discontinued operations, net of taxes	0	0	20	0	0	0	0	0	20	0	0
Net income	265	226	239	176	139	227	233	189	906	788	824
Less: net income attributable to noncontrolling interests	12	11	13	12	12	14	14	12	48	52	52
Net income attributable to Quest Diagnostics	$ 253	$ 215	$ 226	$ 164	$ 127	$ 213	$ 219	$ 177	858	736	772
Depreciation and amortization									329	309	270
Total capital expenditures									400	383	252
Routine clinical testing services
Segment Reporting Information [Line Items]
Total net revenues									4,206	4,217	4,006
Gene-based and esoteric (including advanced diagnostics) testing services
Segment Reporting Information [Line Items]
Total net revenues									2,620	2,409	2,449
Anatomic pathology testing services
Segment Reporting Information [Line Items]
Total net revenues									579	578	612
All other services
Segment Reporting Information [Line Items]
Total net revenues									$ 321	$ 327	$ 335
DIS business
Segment Reporting Information [Line Items]
Percentage of net revenues from the DIS business									96.00%	96.00%	96.00%
Total net revenues									$ 7,405	$ 7,204	$ 7,068
Total operating income									1,298	1,235	1,313
Depreciation and amortization									226	213	189
Total capital expenditures									373	330	219
All other operating segments
Segment Reporting Information [Line Items]
Total net revenues									321	327	334
Total operating income									42	47	52
Depreciation and amortization									6	6	6
Total capital expenditures									20	16	15
General corporate income (expenses), Net
Segment Reporting Information [Line Items]
Total operating income									(109)	(181)	(200)
Depreciation and amortization									97	90	75
Total capital expenditures									$ 7	$ 37	$ 18
Minimum | DIS business
Segment Reporting Information [Line Items]
Percentage of net revenues from the DIS business									95.00%	95.00%	95.00%