Summary of Significant Accounting Policies Additional Details (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($)
Accounting Policies [Abstract]
Statement of cash flows reclassification from operating activities to investing activities	$ 254

Statement of cash flows reclassification from operating activities to investing activities

No definition available.

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Namespace Prefix:	gild_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration