EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Amounts attributable to Quest Diagnostics’ common stockholders:
Net income attributable to Quest Diagnostics		$ 631	$ 185	$ 1,100	$ 284
Less: Earnings allocated to participating securities		3	1	4	1
Earnings available to Quest Diagnostics’ common stockholders – basic and diluted		$ 628	$ 184	$ 1,096	$ 283
Weighted average common shares outstanding - basic		125	134	129	134
Stock options and performance share units		2	2	2	1
Weighted average common shares outstanding - diluted		127	136	131	135
Basic(in dollars per share)		$ 5.05	$ 1.38	$ 8.52	$ 2.12
Diluted (in dollars per share)		$ 4.96	$ 1.36	$ 8.38	$ 2.09
Stock options and performance share units		1	1	1	2
ASRs
Accelerated Share Repurchases [Line Items]
Accelerated share repurchases price paid	$ 1,500