v3.8.0.1

Employee Benefit Plans - Deferred Comp Narrative (Details) - Deferred compensation plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jan. 01, 2017
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Employer contribution vesting percent upon the occurrence of participant's disability, death or retirement or change in control of the Company	100.00%
Deferred compensation plan assets	$ 35	$ 31
Deferred compensation liability	$ 33	$ 29
Senior level employee [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Percent of base salary available for contribution to the deferred compensation plan	80.00%
Percent of all other forms of compensation available for contribution to the deferred compensation plan	100.00%
Director [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Percent of all other forms of compensation available for contribution to the deferred compensation plan	100.00%

X

- Definition

Deferred Compensation Arrangement With Individual, Vesting Percent, Specified Events

+ References

No definition available.

+ Details

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Balance Type:	na
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X

- Definition

Deferred Compensation Plan, Maximum Annual Contributions Per Employee, Base Salary, Percent

+ References

No definition available.

+ Details

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Namespace Prefix:	ilmn_
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Balance Type:	na
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X

- Definition

Deferred Compensation Plan, Maximum Annual Contributions Per Employee, Other Compensation, Percent

+ References

No definition available.

+ Details

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Namespace Prefix:	ilmn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

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Data Type:	xbrli:stringItemType
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X

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements. Represents currently earned compensation under cash arrangements (such as a profit-sharing plan, rabbi trust, and employee contract--excluding equity-based arrangements) that is not actually paid until a later date.

+ References

No definition available.

+ Details

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

X

- Definition

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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X

- Details

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Namespace Prefix:
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Period Type:

X

- Details

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Namespace Prefix:
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Period Type: