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

X
- Definition Deferred Compensation Plan, Maximum Annual Contributions Per Employee, Base Salary, Percent + References No definition available. + Details
Name: | ilmn_DeferredCompensationPlanMaximumAnnualContributionsPerEmployeeBaseSalaryPercent
Namespace Prefix: | ilmn_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Deferred Compensation Plan, Maximum Annual Contributions Per Employee, Other Compensation, Percent + References No definition available. + Details
Name: | ilmn_DeferredCompensationPlanMaximumAnnualContributionsPerEmployeeOtherCompensationPercent
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
Name: | us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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
Name: | us-gaap_DeferredCompensationCashbasedArrangementsLiabilityCurrentAndNoncurrent
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
Name: | us-gaap_DeferredCompensationPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationExcludingShareBasedPaymentsAndRetirementBenefitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TitleOfIndividualAxis=ilmn_SeniorLevelEmployeeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TitleOfIndividualAxis=us-gaap_DirectorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |