Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 03, 2021 USD ($)	Sep. 27, 2020 USD ($)	Oct. 03, 2021 USD ($) segment	Sep. 27, 2020 USD ($)	Jan. 03, 2021 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			2
Segment Reporting Information [Line Items]
Consolidated revenue	$ 1,108	$ 794	$ 3,327	$ 2,286
Consolidated depreciation and amortization	65	46	162	137
Consolidated (loss) income from operations	(545)	162	(164)	447
Consolidated total assets	15,063		15,063		$ 7,585
Total net long-lived assets	1,685		1,685		1,454
United States
Segment Reporting Information [Line Items]
Total net long-lived assets	1,300		1,300		1,134
Singapore
Segment Reporting Information [Line Items]
Total net long-lived assets	204		204		150
United Kingdom
Segment Reporting Information [Line Items]
Total net long-lived assets	138		138		141
Other countries
Segment Reporting Information [Line Items]
Total net long-lived assets	43		43		29
Core Illumina
Segment Reporting Information [Line Items]
Consolidated revenue	1,106	794	3,325	2,286
Consolidated depreciation and amortization	51	46	148	137
Consolidated (loss) income from operations	205	162	586	447
GRAIL
Segment Reporting Information [Line Items]
Consolidated revenue	2	0	2	0
Consolidated depreciation and amortization	14	0	14	0
Consolidated (loss) income from operations	(750)	$ 0	(750)	$ 0
Operating Segments | Core Illumina
Segment Reporting Information [Line Items]
Consolidated total assets	5,794		5,794		7,585
Operating Segments | GRAIL
Segment Reporting Information [Line Items]
Consolidated total assets	9,270		9,270		0
Elimination of intersegment
Segment Reporting Information [Line Items]
Consolidated total assets	$ (1)		$ (1)		$ 0