Quarterly Operating Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Net revenues	$ 1,849	$ 1,880	$ 1,925	$ 1,839	$ 1,883	$ 1,904	$ 1,902	$ 1,746	$ 7,493	$ 7,435	$ 7,146
Gross profit	699	718	743	676	699	726	728	645	2,836	2,798
Income from continuing operations	200	354	129	70	195	139	142	111	753	587	848
Income (loss) from discontinued operations, net of taxes	0	0	0	0	5	0	0	0	0	5	35
Net income	200	354	129	70	200	139	142	111	753	592	883
Less: net income attributable to noncontrolling interests	12	12	11	9	10	10	9	7	44	36	34
Net income attributable to Quest Diagnostics	188	342	118	61	190	129	133	104	709	556	849
Income from continuing operations	$ 188	$ 342	$ 118	$ 61	$ 185	$ 129	$ 133	$ 104	$ 709	$ 551	$ 814
Income from continuing operations	$ 1.31	$ 2.37	$ 0.82	$ 0.42	$ 1.27	$ 0.89	$ 0.92	$ 0.72	$ 4.92	$ 3.80	$ 5.35
Income (loss) from discontinued operations, per basic share	0.00	0.00	0.00	0.00	0.03	0.00	0.00	0.00	0.00	0.03	0.23
Net income	1.31	2.37	0.82	0.42	1.30	0.89	0.92	0.72	4.92	3.83	5.58
Income from continuing operations	1.29	2.35	0.81	0.42	1.26	0.88	0.92	0.71	4.87	3.78	5.31
Income (loss) from discontinued operations, per diluted share	0.00	0.00	0.00	0.00	0.03	0.00	0.00	0.00	0.00	0.03	0.23
Net income	$ 1.29	$ 2.35	$ 0.81	$ 0.42	$ 1.29	$ 0.88	$ 0.92	$ 0.71	$ 4.87	$ 3.81	$ 5.54