EARNINGS (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Earnings Per Share, Basic and Diluted [Abstract]
Income from continuing operations	$ 254	$ 161	$ 193	$ 164	$ 155	$ 192	$ 195	$ 103	$ 772	$ 645	$ 709
Less: Earnings allocated to participating securities									3	3	3
Earnings available to Quest Diagnostics' common stockholders - basic and diluted									$ 769	$ 642	$ 706
Weighted average common shares outstanding - basic									137	140	144
Stock options and performance share units									3	2	1
Weighted average common shares outstanding - diluted									140	142	145
Basic (in dollars per share)	$ 1.86	$ 1.18	$ 1.40	$ 1.19	$ 1.11	$ 1.37	$ 1.38	$ 0.72	$ 5.63	$ 4.58	$ 4.92
Net income, per diluted share (in dollars per share)	$ 1.82	$ 1.15	$ 1.37	$ 1.16	$ 1.09	$ 1.34	$ 1.37	$ 0.71	$ 5.50	$ 4.51	$ 4.87
Stock options and performance share units not included due to their antidilutive effect									2	1	2