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Inventories - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Schedule of Inventory [Line Items]
Inventory write-downs		$ 649	$ 572
Inventory Write-downs for Excess Raw Materials
Schedule of Inventory [Line Items]
Inventory write-downs	$ 500	$ 547	$ 440

X

- Definition

[Line Items] for Disclosure of information about inventory.

+ References

No definition available.

+ Details

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Namespace Prefix:	gild_
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X

- Definition

Amount of loss from reductions in inventory due to subsequent measurement adjustments, including, but not limited to, physical deterioration, obsolescence, or changes in price levels.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116847112&loc=d3e4542-108314

+ Details

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Balance Type:	debit
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X

- Details

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