Quarterly Operating Results (unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data [Abstract]
Net revenues	$ 1,936	$ 1,931	$ 1,943	$ 1,899	$ 1,861	$ 1,885	$ 1,906	$ 1,863	$ 7,709	$ 7,515	$ 7,493
Gross profit	742	741	773	734	701	728	751	719	2,990	2,899
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
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
Diluted (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