BUSINESS SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Percentage of net revenues from the DIS business									90.00%	90.00%	90.00%
Total net revenues	$ 1,936	$ 1,931	$ 1,943	$ 1,899	$ 1,861	$ 1,885	$ 1,906	$ 1,863	$ 7,709	$ 7,515	$ 7,493
Total operating income									1,165	1,277	1,399
Non-operating expenses, net									(135)	(191)	(296)
Income before income taxes and equity in earnings of equity method investees									1,030	1,086	1,103
Income tax expense									(241)	(429)	(373)
Equity in earnings of equity method investees, net of taxes									35	39	23
Net income	267	175	207	175	167	205	209	115	824	696	753
Less: net income attributable to noncontrolling interests	13	14	14	11	12	13	14	12	52	51	44
Net income attributable to Quest Diagnostics	$ 254	$ 161	$ 193	$ 164	$ 155	$ 192	$ 195	$ 103	772	645	709
Depreciation and amortization									270	249	304
Total capital expenditures									252	293	263
Routine clinical testing services [Member]
Segment Reporting Information [Line Items]
Total net revenues									4,309	4,179	4,078
Gene-based and esoteric (including advanced diagnostics) testing services [Member]
Segment Reporting Information [Line Items]
Total net revenues									2,449	2,335	2,256
Anatomic pathology testing services [Member]
Segment Reporting Information [Line Items]
Total net revenues									612	624	631
All other services [Member]
Segment Reporting Information [Line Items]
Total net revenues									339	377	528
DIS business [Member]
Segment Reporting Information [Line Items]
Total net revenues									7,370	7,138	6,965
Total operating income									1,313	1,244	1,118
Depreciation and amortization									189	170	212
Total capital expenditures									219	264	243
All other operating segments [Member]
Segment Reporting Information [Line Items]
Total net revenues									339	377	528
Total operating income									52	64	110
Depreciation and amortization									6	6	10
Total capital expenditures									15	21	16
General corporate income (expenses), Net [Member]
Segment Reporting Information [Line Items]
Total operating income									(200)	(31)	171
Depreciation and amortization									75	73	82
Total capital expenditures									$ 18	$ 8	$ 4