EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Amounts attributable to Quest Diagnostics’ common stockholders:
Net income attributable to Quest Diagnostics		$ 505	$ 568	$ 1,605	$ 852
Less: Earnings allocated to participating securities		2	2	6	3
Earnings available to Quest Diagnostics’ common stockholders – basic and diluted		$ 503	$ 566	$ 1,599	$ 849
Weighted average common shares outstanding - basic		123	135	127	134
Stock options and performance share units		2	2	2	2
Weighted average common shares outstanding - diluted		125	137	129	136
Basic(in dollars per share)		$ 4.11	$ 4.20	$ 12.63	$ 6.33
Diluted (in dollars per share)		$ 4.02	$ 4.14	$ 12.41	$ 6.25
Stock options and performance share units		0	1	0	1
ASRs
Accelerated Share Repurchases [Line Items]
Accelerated share repurchases price paid	$ 1,500