Quarterly Operating Results (unaudited) (Schedule) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data [Abstract]
Net revenues	$ 1,926	$ 1,956	$ 1,953	$ 1,891	$ 1,839	$ 1,889	$ 1,919	$ 1,884	$ 7,726	$ 7,531	$ 7,402
Gross profit	662	692	688	647	604	667	676	658	2,689	2,605
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
Earnings per share attributable to Quest Diagnostics’ common stockholders - basic:
Income from continuing operations (in dollars per share)	$ 1.88	$ 1.59	$ 1.52	$ 1.22	$ 0.93	$ 1.56	$ 1.60	$ 1.30	$ 6.21	$ 5.39	$ 5.63
Income from discontinued operations (in dollars per share)	0	0	0.15	0	0	0	0	0	0.15	0	0
Net income (in dollars per share)	1.88	1.59	1.67	1.22	0.93	1.56	1.60	1.30	6.36	5.39	5.63
Earnings per share attributable to Quest Diagnostics’ common stockholders - diluted:
Income from continuing operations (in dollars per share)	1.86	1.56	1.51	1.20	0.92	1.53	1.57	1.27	6.13	5.29	5.50
Income from discontinued operations (in dollars per share)	0	0	0.15	0	0	0	0	0	0.15	0	0
Net income (in dollars per share)	$ 1.86	$ 1.56	$ 1.66	$ 1.20	$ 0.92	$ 1.53	$ 1.57	$ 1.27	$ 6.28	$ 5.29	$ 5.50