v3.8.0.1
Balance Sheet Account Details - Narrative - Deconsolidation of GRAIL, Inc. (Details) - USD ($)
shares in Millions, $ in Millions
1 Months Ended 2 Months Ended 3 Months Ended 12 Months Ended
Feb. 28, 2017
Jan. 31, 2016
Feb. 28, 2017
Jul. 02, 2017
Dec. 31, 2017
Jan. 01, 2017
Jan. 03, 2016
Feb. 27, 2017
Variable Interest Entity [Line Items]                
Proceeds from sale of GRAIL preferred stock         $ 278      
Payments for additional GRAIL shares purchased by Illumina         29 $ 14 $ 6  
Gain on deconsolidation of GRAIL $ 453       $ 453      
Portion of gain on deconsolidation related to remeasurement of Company's retained equity interest $ 159              
GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Cost-method investment ownership percentage 19.00%   19.00% 17.00%        
Cost-method investment voting interest percentage 13.00%   13.00% 12.00%        
GRAIL Class B [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Strategic Investment Shares Purchased       3        
Payments for additional GRAIL shares purchased by Illumina       $ 14        
Remaining shares of GRAIL owned by Illumina         3      
GRAIL Class A Preferred [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Remaining shares of GRAIL owned by Illumina         5      
GRAIL Class A Common [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Remaining shares of GRAIL owned by Illumina         78      
Variable Interest Entity, Primary Beneficiary [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
GRAIL Series B preferred financing   $ 120            
Proceeds from sale of GRAIL preferred stock $ 278              
Equity ownership interest percentage               52.00%
Percentage of entity's losses absorbed     50.00%          
Variable Interest Entity, Primary Beneficiary [Member] | GRAIL Class B [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
GRAIL Series B preferred financing $ 900              
Variable Interest Entity, Primary Beneficiary [Member] | GRAIL Class A Preferred [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Shares repurchased by GRAIL from Illumina 35              
Variable Interest Entity, Primary Beneficiary [Member] | GRAIL Class A-1 Convertible [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Shares repurchased by GRAIL from Illumina 34              
Other Assets [Member]                
Variable Interest Entity [Line Items]                
Cost-method investments         $ 250 $ 57    
Other Assets [Member] | GRAIL, Inc. [Member]                
Variable Interest Entity [Line Items]                
Cost-method investments         $ 185