v3.8.0.1

Organization and Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Major Classes of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Building and leasehold improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life	4 years
Building and leasehold improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life	30 years
Machinery and equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life	3 years
Machinery and equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life	5 years
Computer hardware and software [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life	3 years
Computer hardware and software [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life	7 years
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Useful life	7 years

X

- 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

Name:	us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ilmn_BuildingandLeaseholdImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_MachineryAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ComputerEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: