FINANCIAL INSTRUMENTS (Balance Sheets) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Long-Term Debt	$ (33)
Hedging adjustment on a discontinued relationship	56
Long-term Debt [Member] \| Fair Value Hedging [Member]
Derivative [Line Items]
Carrying Amount of Hedged Long-Term Debt	1,132
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Long-Term Debt	$ (33)

Debt Instrument, fair value basis adjustment attributable to hedged debt

No definition available.

Name:	dgx_DebtInstrumentFairValueBasisAdjustmentAttributableToHedgedDebt
Namespace Prefix:	dgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective fair value hedge that is amortized upon discontinuation of the fair value hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 35
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=82917030&loc=d3e75592-113984

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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- Details

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