EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Net income attributable to Quest Diagnostics	$ 213	$ 161	$ 609	$ 518
Less: Earnings allocated to participating securities	1	1	2	2
Earnings available to Quest Diagnostics' common stockholders - basic and diluted	$ 212	$ 160	$ 607	$ 516
Weighted average common shares outstanding - basic	136	137	136	137
Stock options and performance share units	3	3	3	3
Weighted average common shares outstanding - diluted	139	140	139	140
Basic (per share)	$ 1.56	$ 1.18	$ 4.46	$ 3.77
Diluted (per share)	$ 1.53	$ 1.15	$ 4.37	$ 3.68
Stock options and performance share units not included due to their antidilutive effect	2	2	2	1

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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