Document and Entity Information - shares shares in Millions	6 Months Ended
Document and Entity Information - shares shares in Millions	Jul. 01, 2018	Jul. 27, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Illumina Inc
Entity Central Index Key	0001110803
Current Fiscal Year End Date	--12-30
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jul. 01, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		147

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 1,344	$ 1,225
Short-term investments	1,168	920
Accounts receivable, net	395	411
Inventory	362	333
Prepaid expenses and other current assets	68	91
Total current assets	3,337	2,980
Property and equipment, net	1,036	931
Goodwill	831	771
Intangible assets, net	205	175
Deferred tax assets	108	88
Other assets	334	312
Total assets	5,851	5,257
Current liabilities:
Accounts payable	149	160
Accrued liabilities	422	432
Build-to-suit lease liability	21	144
Long-term debt, current portion	625	10
Total current liabilities	1,217	746
Long-term debt	723	1,182
Other long-term liabilities	343	360
Redeemable noncontrolling interests	217	220
Stockholders’ equity:
Preferred stock	0	0
Common stock	2	2
Additional paid-in capital	2,939	2,833
Accumulated other comprehensive loss	(1)	(1)
Retained earnings	2,673	2,256
Treasury stock, at cost	(2,356)	(2,341)
Total Illumina stockholders’ equity	3,257	2,749
Noncontrolling interests	94
Total stockholders’ equity	3,351	2,749
Total liabilities and stockholders’ equity	$ 5,851	$ 5,257

Condensed Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Revenue:
Product revenue	$ 673	$ 543	$ 1,301	$ 1,034
Service and other revenue	157	119	311	227
Total revenue	830	662	1,612	1,261
Cost of revenue:
Cost of product revenue	181	168	355	334
Cost of service and other revenue	65	50	127	104
Amortization of acquired intangible assets	9	10	17	21
Total cost of revenue	255	228	499	459
Gross profit	575	434	1,113	802
Operating expense:
Research and development	151	130	288	275
Selling, general and administrative	197	161	380	332
Total operating expense	348	291	668	607
Income from operations	227	143	445	195
Other income (expense):
Interest income	11	5	16	9
Interest expense	(11)	(8)	(22)	(16)
Other income, net	5	1	14	457
Total other income (expense), net	5	(2)	8	450
Income before income taxes	232	141	453	645
Provision for income taxes	32	21	56	177
Consolidated net income	200	120	397	468
Add: Net loss attributable to noncontrolling interests	9	8	20	27
Net income attributable to Illumina stockholders	209	128	417	495
Net income attributable to Illumina stockholders for earnings per share	$ 209	$ 128	$ 417	$ 494
Earnings per share attributable to Illumina stockholders:
Basic (in dollars per share)	$ 1.42	$ 0.87	$ 2.84	$ 3.38
Diluted (in dollars per share)	$ 1.41	$ 0.87	$ 2.82	$ 3.35
Shares used in computing earnings per share:
Basic (in shares)	147	146	147	146
Diluted (in shares)	148	147	148	147

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Statement of Comprehensive Income [Abstract]
Consolidated net income	$ 200	$ 120	$ 397	$ 468
Unrealized gain on available-for-sale debt securities, net of deferred tax		1		1
Total consolidated comprehensive income	200	121	397	469
Add: Comprehensive loss attributable to noncontrolling interests	9	8	20	27
Comprehensive income attributable to Illumina stockholders	$ 209	$ 129	$ 417	$ 496

Condensed Consolidated Statement of Stockholders' Equity Statement - 6 months ended Jul. 01, 2018 - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Treasury Stock	Noncontrolling Interests
Beginning balance at Dec. 31, 2017	$ 2,749	$ 2	$ 2,833	$ (1)	$ 2,256	$ (2,341)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	414				417		(3)
Issuance of common stock, net of repurchases	7		22			(15)
Share-based compensation	98		98
Adjustment to the carrying value of redeemable noncontrolling interests	(13)		(13)
Contributions from noncontrolling interest owners	92						92
Issuance of subsidiary shares	5						5
Vesting of redeemable equity awards	(1)		(1)
Ending balance at Jul. 01, 2018	$ 3,351	$ 2	$ 2,939	$ (1)	$ 2,673	$ (2,356)	$ 94

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017
Cash flows from operating activities:
Consolidated net income	$ 397	$ 468
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on deconsolidation of GRAIL		(453)
Depreciation expense	65	52
Amortization of intangible assets	19	24
Share-based compensation expense	98	89
Accretion of debt discount	16	15
Deferred income taxes	(22)	66
Impairment of intangible assets		23
Other	(6)	(5)
Changes in operating assets and liabilities:
Accounts receivable	12	14
Inventory	(28)	(9)
Prepaid expenses and other current assets	1	5
Other assets	(5)	(3)
Accounts payable	1
Accrued liabilities	17	41
Other long-term liabilities	(15)	19
Net cash provided by operating activities	550	346
Cash flows from investing activities:
Purchases of available-for-sale securities	(1,137)	(86)
Sales of available-for-sale securities	332	139
Maturities of available-for-sale securities	556	96
Net cash paid for acquisitions	(100)
Proceeds from sale of GRAIL securities		278
Deconsolidation of GRAIL cash		(52)
Net purchases of strategic investments	(9)	(25)
Purchases of property and equipment	(167)	(152)
Net cash (used in) provided by investing activities	(525)	198
Cash flows from financing activities:
Payments on financing obligations	(2)	(6)
Payments on acquisition related contingent consideration liability		(3)
Proceeds from issuance of debt		5
Common stock repurchases		(101)
Taxes paid related to net share settlement of equity awards	(15)	(24)
Proceeds from issuance of common stock	22	31
Contributions from noncontrolling interest owners	92	36
Net cash provided by (used in) financing activities	97	(62)
Effect of exchange rate changes on cash and cash equivalents	(3)	2
Net increase in cash and cash equivalents	119	484
Cash and cash equivalents at beginning of period	1,225	735
Cash and cash equivalents at end of period	$ 1,344	$ 1,219

Basis of Presentation and Summary of Significant Accounting Policies

6 Months Ended

Jul. 01, 2018

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Interim financial results are not necessarily indicative of results anticipated for the full year. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and footnotes included in the Annual Report on Form 10-K for the fiscal year ended December 31, 2017, from which the prior year balance sheet information herein was derived. The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue, and expense, and related disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

The unaudited condensed consolidated financial statements include our accounts, our wholly-owned subsidiaries, majority-owned or controlled companies, and variable interest entities (VIEs) for which we are the primary beneficiary. All intercompany transactions and balances have been eliminated in consolidation. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented.

We evaluate our ownership, contractual, and other interests in entities that are not wholly-owned to determine if these entities are VIEs, and, if so, whether we are the primary beneficiary of the VIE. In determining whether we are the primary beneficiary of a VIE and therefore required to consolidate the VIE, a qualitative approach is applied that determines whether we have both (1) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and (2) the obligation to absorb losses of, or the rights to receive benefits from, the VIE that could potentially be significant to that VIE. We continuously assess whether we are the primary beneficiary of a VIE, as changes to existing relationships or future transactions may result in the consolidation or deconsolidation of such VIE. During the six months ended July 1, 2018, our consolidated VIE, Helix, received additional cash contributions from us and third-party investors in exchange for voting equity interests in Helix. Therefore, we reassessed and concluded that Helix continued to be a variable interest entity and that we remained the primary beneficiary. During the periods presented, we have not provided any other financial or other support to our VIEs that we were not contractually required to provide.

The equity method is used to account for investments in which we have the ability to exercise significant influence, but not control, over the investee. Such investments are recorded within other assets, and the share of net income or losses of equity investments is recognized on a one quarter lag in other income, net.

Redeemable Noncontrolling Interests

Noncontrolling interests represent the portion of equity (net assets) in Helix, our consolidated but not wholly-owned entity, that is neither directly nor indirectly attributable to us. Noncontrolling interests with embedded contingent redemption features, such as put rights, that are not solely within our control are considered redeemable noncontrolling interests. Redeemable noncontrolling interests are presented outside of stockholders’ equity on the condensed consolidated balance sheets.

Fiscal Year

Our fiscal year is the 52 or 53 weeks ending the Sunday closest to December 31, with quarters of 13 or 14 weeks ending the Sunday closest to March 31, June 30, September 30, and December 31. The three and six months ended July 1, 2018 and July 2, 2017 were both 13 and 26 weeks, respectively.

Reclassifications

Certain prior period amounts have been reclassified to conform to the current period presentation.

Significant Accounting Policies

During the three and six months ended July 1, 2018, there have been no changes to our significant accounting policies as described in our Annual Report on Form 10-K for the fiscal year ended December 31, 2017, except as described below.

Recently Adopted Accounting Pronouncements

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). The new standard is based on the principle that revenue should be recognized in an amount that reflects the consideration to which we expect to be entitled in exchange for the transfer of promised goods or services. We adopted Topic 606 using the modified retrospective transition method. The cumulative effect of applying the new revenue standard to all incomplete contracts as of January 1, 2018 was not material and, therefore, did not result in an adjustment to retained earnings. There was no material difference to the condensed consolidated financial statements for the three and six months ended July 1, 2018 due to the adoption of Topic 606.

In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10), which requires equity investments (other than those accounted for under the equity method or those that result in consolidation) to be measured at fair value, with changes in fair value recognized in net income. This standard was effective for us beginning in the first quarter of 2018. Based on our elections, our strategic equity investments that do not have readily determinable fair values and do not qualify for the net asset value practical expedient for estimating fair value are measured at cost, less any impairments, plus or minus changes resulting from observable price changes in orderly transactions for identifiable or similar investments of the same issuer. The measurement alternative was applied prospectively and did not result in an adjustment to retained earnings.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). The new standard requires lessees to recognize most leases on their balance sheet as lease liabilities with corresponding right-of-use assets. ASU 2016-02 is effective for us beginning in the first quarter of 2019. Currently, the standard will be adopted on a modified retrospective transition basis for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The FASB has proposed an alternative method to adopt the lease standard by recognizing a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We plan to utilize this alternative adoption method, if finalized by the FASB. In order to adopt the new standard in the first quarter of fiscal 2019, we are currently designing and implementing changes to our systems, processes, policies, and controls for lease accounting. We expect to elect the standard’s package of practical expedients on adoption, which allows us to carry forward our historical assessment of whether existing agreements contain a lease and the classification of our existing lease agreements. We do not expect to elect the standard’s available hindsight practical expedient on adoption. While we continue to review our existing lease agreements and assess the effects of adoption, we believe the new standard will have a material effect on our consolidated financial statements and disclosures. We expect substantially all of our real-estate operating lease commitments will be recognized as lease liabilities with corresponding right-of-use assets upon adoption, resulting in a significant increase in the assets and liabilities on the consolidated balance sheet. We are currently evaluating the impact of Topic 842 on the consolidated financial statements as it relates to other aspects of our business.

In June 2016, the FASB issued Accounting Standards Update (ASU) 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments, which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. The standard is effective for us beginning in the first quarter of 2020, with early adoption permitted. We are currently evaluating the expected impact of ASU 2016-13 on our consolidated financial statements.

Revenue

Our revenue is generated primarily from the sale of products and services. Product revenue primarily consists of sales of instruments and consumables used in genetic analysis. Service and other revenue primarily consists of revenue generated from genotyping and sequencing services and instrument service contracts.

We recognize revenue when control of our products and services is transferred to our customers in an amount that reflects the consideration we expect to receive from our customers in exchange for those products and services. This process involves identifying the contract with a customer, determining the performance obligations in the contract, determining the contract price, allocating the contract price to the distinct performance obligations in the contract, and recognizing revenue when the performance obligations have been satisfied. A performance obligation is considered distinct from other obligations in a contract when it provides a benefit to the customer either on its own or together with other resources that are readily available to the customer and is separately identified in the contract. We consider a performance obligation satisfied once we have transferred control of a good or service to the customer, meaning the customer has the ability to use and obtain the benefit of the good or service. We recognize revenue for satisfied performance obligations only when we determine there are no uncertainties regarding payment terms or transfer of control.

Revenue from product sales is recognized generally upon delivery to the end customer, which is when control of the product is deemed to be transferred. Invoicing typically occurs upon shipment; the term between invoicing and when payment is due is not significant. In instances where right of payment or transfer of title is contingent upon the customer’s acceptance of the product, revenue is deferred until all acceptance criteria have been met. Revenue from instrument service contracts is recognized as the services are rendered, typically evenly over the contract term. Revenue from genotyping and sequencing services is recognized when earned, which is generally at the time the genotyping or sequencing analysis data is made available to the customer or agreed-upon milestones are reached.

Revenue is recorded net of discounts, distributor commissions, and sales taxes collected on behalf of governmental authorities. Employee sales commissions are recorded as selling, general and administrative expenses when incurred as the amortization period for such costs, if capitalized, would have been one year or less.

We regularly enter into contracts with multiple performance obligations. Such obligations are generally satisfied within a short time frame, approximately three to six months, after the contract execution date. Revenue recognition for contracts with multiple deliverables is based on the separate, distinct performance obligations within the contract. We do not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less, and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed.

The contract price is allocated to each performance obligation in proportion to its standalone selling price. We determine our best estimate of standalone selling price using average selling prices over a rolling 12-month period coupled with an assessment of current market conditions. If the product or service has no history of sales or if the sales volume is not sufficient, we rely upon prices set by our pricing committee, adjusted for applicable discounts.

Contract liabilities, which consist of deferred revenue and customer deposits, as of July 1, 2018 and December 31, 2017 were $196 million and $181 million, respectively, of which the short-term portions of $168 million and $150 million, respectively, were recorded in accrued liabilities and the remaining long-term portions were recorded in other long-term liabilities. Revenue recorded in the three and six months ended July 1, 2018 included $34 million and $102 million of previously deferred revenue that was included in contract liabilities as of December 31, 2017. Contract assets as of July 1, 2018 and December 31, 2017 were not material.

In certain markets, products and services are sold to customers through distributors. In most sales through distributors, the product is delivered directly to customers. The terms of sales transactions through distributors are consistent with the terms of direct sales to customers.

The following tables represent revenue by source (in millions):



	Three Months Ended
	July 1, 2018						July 2, 2017
	Sequencing		Microarray		Total		Sequencing		Microarray		Total
Consumables	$	455	$	85	$	540	$	338	$	64	$	402
Instruments	123		4		127		130		6		136
Other product	6		—		6		5		—		5
Total product revenue	584		89		673		473		70		543
Service and other revenue	106		51		157		77		42		119
Total revenue	$	690	$	140	$	830	$	550	$	112	$	662



	Six Months Ended
	July 1, 2018						July 2, 2017
	Sequencing		Microarray		Total		Sequencing		Microarray		Total
Consumables	$	873	$	172	$	1,045	$	656	$	132	$	788
Instruments	235		9		244		225		11		236
Other product	11		1		12		9		1		10
Total product revenue	1,119		182		1,301		890		144		1,034
Service and other revenue	202		109		311		155		72		227
Total revenue	$	1,321	$	291	$	1,612	$	1,045	$	216	$	1,261

Revenue related to our Consolidated VIEs is included in sequencing services and other revenue.

The following table represents revenue by geographic area, based on region of destination (in millions):



	Three Months Ended				Six Months Ended
	July 1, 2018		July 2, 2017		July 1, 2018		July 2, 2017
United States	$	445	$	374	$	861	$	699
Europe	196		145		380		271
Greater China (1)	107		78		185		134
Asia-Pacific (1)	55		46		125		113
Other markets	27		19		61		44
Total revenue	$	830	$	662	$	1,612	$	1,261

____________________________________

(1) Revenue for the Greater China region, which consists of China, Taiwan, and Hong Kong, is reported separately from the Asia-Pacific region.

Earnings per Share

Basic earnings per share attributable to Illumina stockholders is computed based on the weighted average number of common shares outstanding during the period. Diluted earnings per share attributable to Illumina stockholders is computed based on the sum of the weighted average number of common shares and potentially dilutive common shares outstanding during the period. Per-share earnings of our VIEs are included in the consolidated basic and diluted earnings per share computations based on our share of the VIE’s securities.

Potentially dilutive common shares consist of shares issuable under convertible senior notes and equity awards. Convertible senior notes have a dilutive impact when the average market price of our common stock exceeds the applicable conversion price of the respective notes. Potentially dilutive common shares from equity awards are determined using the average share price for each period under the treasury stock method. In addition, proceeds from exercise of equity awards and the average amount of unrecognized compensation expense for equity awards are assumed to be used to repurchase shares.

The following is the calculation of weighted average shares used to calculate basic and diluted earnings per share (in millions):



	Three Months Ended		Six Months Ended
	July 1, 2018	July 2, 2017	July 1, 2018	July 2, 2017
Weighted average shares outstanding	147	146	147	146
Effect of potentially dilutive common shares from:
Equity awards	1	1	1	1
Weighted average shares used in calculating diluted earnings per share	148	147	148	147

Balance Sheet Account Details

6 Months Ended

Jul. 01, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Account Details

Short-Term Investments

The following is a summary of short-term investments (in millions):



	July 1, 2018							December 31, 2017
	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale debt securities:
Debt securities in government sponsored entities	$	25	$	—		$	25	$	67	$	—		$	67
Corporate debt securities	643		(1		)	642		423		(2		)	421
U.S. Treasury securities	504		(3		)	501		433		(1		)	432
Total available-for-sale debt securities	$	1,172	$	(4	)	$	1,168	$	923	$	(3	)	$	920

Realized gains and losses are determined based on the specific identification method and are reported in interest income.

Contractual maturities of available-for-sale debt securities as of July 1, 2018 were as follows (in millions):



	Estimated Fair Value
Due within one year	$	525
After one but within five years	643
Total	$	1,168

We have the ability, if necessary, to liquidate any of our cash equivalents and short-term investments to meet our liquidity needs in the next 12 months. Accordingly, those investments with contractual maturities greater than one year from the date of purchase are classified as short-term on the accompanying condensed consolidated balance sheets.

Strategic Investments

The carrying amounts of our strategic equity investments without readily determinable fair values are initially measured at cost and are remeasured for impairment and observable price changes in orderly transactions for identifiable or similar investments of the same issuer.

As of July 1, 2018 and December 31, 2017, the aggregate carrying amounts of our strategic equity investments without readily determinable fair values were $263 million and $250 million, respectively, included in other assets. Revenue recognized from transactions with such companies was $36 million and $72 million, respectively, for the three and six months ended July 1, 2018 and $35 million and $58 million, respectively, for the three and six months ended July 2, 2017.

We invest in a venture capital investment fund (the Fund) with a capital commitment of $100 million that is callable over ten years, of which $77 million remains as of July 1, 2018. Our investment in the Fund is accounted for as an equity-method investment. The carrying amounts of the Fund included in other assets were $21 million and $16 million as of July 1, 2018 and December 31, 2017, respectively.

Inventory

Inventory consisted of the following (in millions):



	July 1, 2018		December 31, 2017
Raw materials	$	101	$	93
Work in process	212		188
Finished goods	49		52
Total inventory	$	362	$	333

Property and Equipment

Property and equipment, net consisted of the following (in millions):



	July 1, 2018			December 31, 2017
Leasehold improvements	$	483		$	331
Machinery and equipment	347			316
Computer hardware and software	214			185
Furniture and fixtures	41			34
Buildings	279			155
Construction in progress	148			326
Total property and equipment, gross	1,512			1,347
Accumulated depreciation	(476		)	(416		)
Total property and equipment, net	$	1,036		$	931

Property and equipment, net included non-cash expenditures of $42 million and $94 million for the six months ended July 1, 2018 and July 2, 2017, respectively, which were excluded from the condensed consolidated statements of cash flows. Such non-cash expenditures included $16 million and $60 million recorded under build-to-suit lease accounting for the six months ended July 1, 2018 and July 2, 2017, respectively.

Intangible Assets and Goodwill

On May 14, 2018, we acquired Edico Genome, a provider of data analysis acceleration solutions for next-generation sequencing (NGS) for total cash consideration of $100 million, net of cash acquired. As a result of this transaction, we recorded $56 million as goodwill. In addition, we recorded developed technology of $45 million and a trade name of $1 million, with useful lives of 10 and 3 years, respectively.

We test the carrying value of goodwill in accordance with accounting rules on impairment of goodwill, which require us to estimate the fair value of each reporting unit annually, or when impairment indicators exist, and compare such amounts to their respective carrying values to determine if an impairment is required. We performed the annual assessment for goodwill impairment in the second quarter of 2018, noting no impairment.

Changes to goodwill during the six months ended July 1, 2018 were as follows (in millions):



	Goodwill
Balance as of December 31, 2017	$	771
Current period acquisitions	60
Balance as of July 1, 2018	$	831

We perform regular reviews to determine if any event has occurred that may indicate our identifiable intangible assets are potentially impaired. During the six months ended July 2, 2017, we performed a recoverability test when the planned use of a finite-lived acquired intangible asset changed, resulting in an impairment charge of $18 million recorded in cost of product revenue. Also during the six months ended July 2, 2017, we recorded a $5 million impairment charge in research and development related to an in-process research and development project that was determined to have no future alternative use.

Derivatives

We are exposed to foreign exchange rate risks in the normal course of business. We enter into foreign exchange contracts to manage foreign currency risks related to monetary assets and liabilities that are denominated in currencies other than the U.S. dollar. These foreign exchange contracts are carried at fair value in other current assets or accrued liabilities and are not designated as hedging instruments. Changes in the value of derivatives are recognized in other income, net, along with the remeasurement gain or loss on the foreign currency denominated assets or liabilities.

As of July 1, 2018, we had foreign exchange forward contracts in place to hedge exposures in the euro, Japanese yen, Australian dollar, and Canadian dollar. As of July 1, 2018 and December 31, 2017, the total notional amounts of outstanding forward contracts in place for foreign currency purchases were $95 million and $88 million, respectively.

Accrued Liabilities

Accrued liabilities consisted of the following (in millions):



	July 1, 2018		December 31, 2017
Contract liabilities, current portion	$	168	$	150
Accrued compensation expenses	142		177
Accrued taxes payable	67		50
Other	45		55
Total accrued liabilities	$	422	$	432

Warranties

We generally provide a one-year warranty on instruments. Additionally, we provide a warranty on consumables through the expiration date, which generally ranges from six to twelve months after the manufacture date. At the time revenue is recognized, an accrual is established for estimated warranty expenses based on historical experience as well as anticipated product performance. We periodically review the warranty reserve for adequacy and adjust the warranty accrual, if necessary, based on actual experience and estimated costs to be incurred. Warranty expense is recorded as a component of cost of product revenue.

Changes in the reserve for product warranties during the three and six months ended July 1, 2018 and July 2, 2017 were as follows (in millions):



	Three Months Ended						Six Months Ended
	July 1, 2018			July 2, 2017			July 1, 2018			July 2, 2017
Balance at beginning of period	$	16		$	12		$	17		$	13
Additions charged to cost of product revenue	6			7			12			11
Repairs and replacements	(7		)	(5		)	(14		)	(10		)
Balance at end of period	$	15		$	14		$	15		$	14

Investments in Consolidated VIEs

Helix Holdings I, LLC

In July 2015, we obtained a 50% voting equity ownership interest in Helix Holdings I, LLC (Helix), a limited liability company formed with unrelated third-party investors to pursue the development and commercialization of a marketplace for consumer genomics. We determined that Helix is a VIE as the holders of the at-risk equity investments as a group lack the power to direct the activities of Helix that most significantly impact Helix’s economic performance. Additionally, we determined that we have (a) unilateral power over one of the activities that most significantly impacts the economic performance of Helix through its contractual arrangements and no one individual party has unilateral power over the remaining significant activities of Helix and (b) the obligation to absorb losses of and the right to receive benefits from Helix that are potentially significant to Helix. As a result, we are deemed to be the primary beneficiary of Helix and are required to consolidate Helix.

As contractually committed, in July 2015, we contributed certain perpetual licenses, instruments, intangibles, initial laboratory setup, and discounted supply terms in exchange for voting equity interests in Helix. Such contributions were recorded at their historical basis as they remained within our control. Helix is financed through cash contributions made by us and the third-party investors in exchange for voting equity interests in Helix. During the six months ended July 1, 2018, we made additional investments of $100 million in exchange for voting equity interests in Helix. As of July 1, 2018, the noncontrolling shareholders and Illumina each held 50% of Helix’s outstanding voting equity interests.

Certain noncontrolling Helix investors may require us to redeem certain noncontrolling interests in cash at the then approximate fair market value. Such redemption right is exercisable at the option of certain noncontrolling interest holders after January 1, 2021, provided that a bona fide pursuit of the sale of Helix has occurred and an initial public offering of Helix has not been completed. As the contingent redemption is outside of our control, the redeemable noncontrolling interests in Helix are classified outside of stockholders’ equity on the accompanying condensed consolidated balance sheets. The balance of the redeemable noncontrolling interests is reported at the greater of its carrying value after receiving its allocation of Helix’s profits and losses or its estimated redemption fair value at each reporting date. The fair value of the redeemable noncontrolling interests is considered a Level 3 instrument.

As of July 1, 2018, the accompanying condensed consolidated balance sheet included $171 million of cash and cash equivalents attributable to Helix that will be used to settle its respective obligations and will not be available to settle obligations of Illumina. The remaining assets and liabilities of Helix were not significant to our financial position as of July 1, 2018. Helix had an immaterial impact on our condensed consolidated statements of income and cash flows for the three and six months ended July 1, 2018.

GRAIL, Inc.

In 2016, we obtained a majority equity ownership interest in GRAIL, a company formed with unrelated third-party investors to develop a blood test for early-stage cancer detection. At that time, we determined that GRAIL was a VIE as the entity lacked sufficient equity to finance its activities without additional support. Additionally, we determined that we were the primary beneficiary of GRAIL and were required to consolidate GRAIL. On February 28, 2017, GRAIL completed the initial close of its Series B preferred stock financing, we ceased to have a controlling financial interest in GRAIL, and our equity ownership was reduced from 52% to 19%. Additionally, our voting interest was reduced to 13% and we no longer had representation on GRAIL’s board of directors. As a result, we deconsolidated GRAIL’s financial statements effective February 28, 2017 and recorded a pretax gain on deconsolidation of $453 million in other income, net. The operations of GRAIL from January 2, 2017 up to February 28, 2017, the date of deconsolidation, were included in the accompanying condensed consolidated statements of income for the six months ended July 2, 2017. During this period, we absorbed approximately 50% of GRAIL’s losses based upon our proportional ownership of GRAIL’s common stock.

The carrying value of the investment recorded in other assets was $189 million and $185 million as of July 1, 2018 and December 31, 2017, respectively.

Redeemable Noncontrolling Interests

The activity of the redeemable noncontrolling interests during the six months ended July 1, 2018 was as follows (in millions):



	Redeemable Noncontrolling Interests
Balance as of December 31, 2017	$	220
Vesting of redeemable equity awards	1
Net loss attributable to noncontrolling interests	(17		)
Adjustment up to the redemption value	13
Balance as of July 1, 2018	$	217

Fair Value Measurements

6 Months Ended

Jul. 01, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following table presents the hierarchy for assets and liabilities measured at fair value on a recurring basis as of July 1, 2018 and December 31, 2017 (in millions):



	July 1, 2018								December 31, 2017
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets:
Money market funds (cash equivalents)	$	1,015	$	—	$	—	$	1,015	$	957	$	—	$	—	$	957
Debt securities in government-sponsored entities	—		25		—		25		—		67		—		67
Corporate debt securities	—		642		—		642		—		421		—		421
U.S. Treasury securities	501		—		—		501		432		—		—		432
Deferred compensation plan assets	—		37		—		37		—		35		—		35
Total assets measured at fair value	$	1,516	$	704	$	—	$	2,220	$	1,389	$	523	$	—	$	1,912
Liabilities:
Deferred compensation liability	$	—	$	35	$	—	$	35	$	—	$	33	$	—	$	33

We hold available-for-sale securities that consist of highly-liquid, investment-grade debt securities. We consider information provided by our investment accounting and reporting service provider in the measurement of fair value of our debt securities. The investment service provider provides valuation information from an industry-recognized valuation service. Such valuations may be based on trade prices in active markets for identical assets or liabilities (Level 1 inputs) or valuation models using inputs that are observable either directly or indirectly (Level 2 inputs), such as quoted prices for similar assets or liabilities, yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures. Our deferred compensation plan assets consist primarily of investments in life insurance contracts carried at cash surrender value, which reflects the net asset value of the underlying publicly traded mutual funds. We perform control procedures to corroborate the fair value of our holdings, including comparing valuations obtained from our investment service provider to valuations reported by our asset custodians, validation of pricing sources and models, and review of key model inputs, if necessary.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Debt and Other Commitments

6 Months Ended

Jul. 01, 2018

Debt Disclosure [Abstract]

Debt and Other Commitments

Summary of debt obligations

Debt obligations consisted of the following (dollars in millions):



	July 1, 2018			December 31, 2017
Principal amount of 2019 Notes outstanding	$	633		$	633
Principal amount of 2021 Notes outstanding	517			517
Unamortized discount of liability component of convertible senior notes	(60		)	(75		)
Net carrying amount of liability component of convertible senior notes	1,090			1,075
Obligations under financing leases	254			113
Other	4			4
Less: current portion	(625		)	(10		)
Long-term debt	$	723		$	1,182
Carrying value of equity component of convertible senior notes, net of debt issuance cost	$	161		$	161
Fair value of convertible senior notes outstanding (Level 2)	$	1,427		$	1,305
Weighted-average remaining amortization period of discount on the liability component of convertible senior notes	2.4 years			2.8 years

Convertible Senior Notes

0% Convertible Senior Notes due 2019 (2019 Notes) and 0.5% Convertible Senior Notes due 2021 (2021 Notes)

In June 2014, we issued $633 million aggregate principal amount of 2019 Notes and $517 million aggregate principal amount of 2021 Notes. We used the net proceeds plus cash on hand to repurchase outstanding debt. The 2019 and 2021 Notes mature on June 15, 2019 and June 15, 2021, respectively, and the implied estimated effective rates of the liability components of the Notes were 2.9% and 3.5%, respectively, assuming no conversion.

Both the 2019 and 2021 Notes will be convertible into cash, shares of common stock, or a combination of cash and shares of common stock, at our election, based on an initial conversion rate, subject to adjustment, of 3.9318 shares per $1,000 principal amount of the notes (which represents an initial conversion price of approximately $254.34 per share), only in the following circumstances and to the following extent: (1) during the five business-day period after any 10 consecutive trading day period (the measurement period) in which the trading price per 2019 and 2021 Notes for each day of such measurement period was less than 98% of the product of the last reported sale price of our common stock and the conversion rate on each such day; (2) during any calendar quarter (and only during that quarter) after the calendar quarter ending September 30, 2014, if the last reported sale price of our common stock for 20 or more trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter exceeds 130% of the applicable conversion price in effect on the last trading day of the immediately preceding calendar quarter; (3) upon the occurrence of specified events described in the indenture for the 2019 and 2021 Notes; and (4) at any time on or after March 15, 2019 for the 2019 Notes, or March 15, 2021 for the 2021 Notes, through the second scheduled trading day immediately preceding the maturity date.

During the six months ended July 1, 2018, the market price of our common stock exceeded the conversion price of $254.34 and the potential dilutive impact of the 2019 and 2021 notes has been included in our calculation of diluted earnings per share. Neither the 2019 nor the 2021 Notes were convertible as of July 1, 2018. If the 2019 and 2021 Notes were converted as of July 1, 2018, the if-converted value would exceed the principal amount by $127 million. During the six months ended July 1, 2018, the carrying value of the 2019 Notes was reclassified to short-term as they become convertible within twelve months of the balance sheet date.

Build-to-suit leases

We evaluate whether we are the accounting owner of leased assets during the construction period when we are involved in the construction of leased assets. As of July 1, 2018, we were considered the owner of a construction project for accounting purposes only under build-to-suit lease accounting due to certain indemnification obligations related to the construction. As of July 1, 2018, and December 31, 2017, we recorded $21 million and $144 million, respectively, in project construction costs paid or reimbursed by the landlord as construction in progress and a corresponding build-to-suit lease liability.

During the six months ended July 1, 2018, construction of a build-to-suit property was completed. We concluded we did not qualify for “sale-leaseback” treatment and the lease is accounted for as a financing obligation. Accordingly, $142 million of construction in progress and build-to-suit lease liability were reclassified to building asset and obligations under financing leases, respectively.

Share-based Compensation Expense

6 Months Ended

Jul. 01, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-based Compensation Expense

Share-based compensation expense reported in our statements of income was as follows (in millions):



	Three Months Ended						Six Months Ended
	July 1, 2018			July 2, 2017			July 1, 2018			July 2, 2017
Cost of product revenue	$	4		$	3		$	8		$	6
Cost of service and other revenue	1			1			2			1
Research and development	15			12			30			26
Selling, general and administrative	30			23			58			56
Share-based compensation expense before taxes	50			39			98			89
Related income tax benefits	(11		)	(12		)	(21		)	(23		)
Share-based compensation expense, net of taxes	$	39		$	27		$	77		$	66

The assumptions used for the specified reporting periods and the resulting estimates of weighted-average fair value per share for stock purchased under the Employee Stock Purchase Plan (ESPP) during the six months ended July 1, 2018 were as follows:



	Employee Stock Purchase Rights
Risk-free interest rate	1.22% - 1.89%
Expected volatility	29% - 39%
Expected term	0.5 - 1.0 year
Expected dividends	0		%
Weighted-average fair value per share	$	58.09

As of July 1, 2018, approximately $328 million of unrecognized compensation cost related to restricted stock and ESPP shares granted to date was expected to be recognized over a weighted-average period of approximately 2.3 years.

Stockholders' Equity

6 Months Ended

Jul. 01, 2018

Equity [Abstract]

Stockholders' Equity

Stockholders’ Equity

As of July 1, 2018, approximately 5.5 million shares remained available for future grants under the 2015 Stock Plan.

Restricted Stock

Restricted stock activity and related information for the six months ended July 1, 2018 was as follows (units in thousands):



	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		Weighted-Average Grant-Date Fair Value per Share
	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		RSU		PSU
Outstanding at December 31, 2017	2,085		542		$	172.92	$	166.15
Awarded	60		172		$	257.00	$	170.08
Vested	(103	)	—		$	159.10	—
Cancelled	(132	)	(20	)	$	169.22	$	163.78
Outstanding at July 1, 2018	1,910		694		$	176.56	$	167.19

______________________________________


(1)	The number of units reflect the estimated number of shares to be issued at the end of the performance period.

Stock Options

Stock option activity during the six months ended July 1, 2018 was as follows:



	Options (in thousands)		Weighted-Average Exercise Price
Outstanding at December 31, 2017	322		$	46.93
Exercised	(63	)	$	34.15
Outstanding and exercisable at July 1, 2018	259		$	50.01

ESPP

The price at which common stock is purchased under the ESPP is equal to 85% of the fair market value of the common stock on the first day of the offering period or purchase date, whichever is lower. During the six months ended July 1, 2018, approximately 0.1 million shares were issued under the ESPP. As of July 1, 2018, there were approximately 13.9 million shares available for issuance under the ESPP.

Share Repurchases

On July 28, 2016, our Board of Directors authorized a share repurchase program, which superseded all prior and available repurchase authorizations, to repurchase $250 million of outstanding common stock. During the year ended December 31, 2017, we repurchased 0.6 million shares for $101 million, completing the share repurchase program.

On May 4, 2017, our Board of Directors authorized a share repurchase program to repurchase $250 million of outstanding common stock. During the year ended December 31, 2017, we repurchased 0.8 million shares for $150 million from this program.

On May 1, 2018, our Board of Directors authorized an additional share repurchase program to repurchase $150 million of outstanding common stock. The repurchases may be completed under a 10b5-1 plan or at management’s discretion. Authorizations to repurchase $250 million of our common stock remained available as of July 1, 2018.

Income Taxes	6 Months Ended
Income Taxes	Jul. 01, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Our effective tax rate may vary from the U.S. federal statutory tax rate due to the change in the mix of earnings in tax jurisdictions with different statutory rates, benefits related to tax credits, and the tax impact of non-deductible expenses and other permanent differences between income before income taxes and taxable income. The effective tax rates for the three and six months ended July 1, 2018 were 13.9% and 12.3%, respectively. For the three and six months ended July 1, 2018, the variance from the U.S. federal statutory tax rate of 21% was primarily attributable to the mix of earnings in jurisdictions with lower statutory tax rates than the U.S. federal statutory tax rate, such as in Singapore and the United Kingdom. For the six months ended July 1, 2018, the decrease from the federal statutory rate was also attributable to the discrete tax benefit associated with the recognition of prior year losses from our investment in Helix. We continue to evaluate the impacts of U.S. Tax Reform as we interpret the legislation, including the newly-enacted global intangible low-taxed income (GILTI) provisions which subject our foreign earnings to a minimum level of tax. Because of the complexities of the new legislation, we have not yet elected an accounting policy for GILTI and, therefore, have only included GILTI related to current year operations in our estimated provision for income taxes. Recent FASB guidance indicates that accounting for GILTI either as part of deferred taxes or as a period cost is acceptable. Once further information is gathered and interpretation and analysis of the tax legislation evolves, we will make an appropriate accounting method election.

Legal Proceedings	6 Months Ended
Legal Proceedings	Jul. 01, 2018
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings	Legal Proceedings We are involved in various lawsuits and claims arising in the ordinary course of business, including actions with respect to intellectual property, employment, and contractual matters. In connection with these matters, we assess, on a regular basis, the probability and range of possible loss based on the developments in these matters. A liability is recorded in the financial statements if it is believed to be probable that a loss has been incurred and the amount of the loss can be reasonably estimated. Because litigation is inherently unpredictable and unfavorable results could occur, assessing contingencies is highly subjective and requires judgments about future events. We regularly review outstanding legal matters to determine the adequacy of the liabilities accrued and related disclosures. The amount of ultimate loss may differ from these estimates. Each matter presents its own unique circumstances, and prior litigation does not necessarily provide a reliable basis on which to predict the outcome, or range of outcomes, in any individual proceeding. Because of the uncertainties related to the occurrence, amount, and range of loss on any pending litigation or claim, we are currently unable to predict their ultimate outcome, and, with respect to any pending litigation or claim where no liability has been accrued, to make a meaningful estimate of the reasonably possible loss or range of loss that could result from an unfavorable outcome. In the event opposing litigants in outstanding litigations or claims ultimately succeed at trial and any subsequent appeals on their claims, any potential loss or charges in excess of any established accruals, individually or in the aggregate, could have a material adverse effect on our business, financial condition, results of operations, and/or cash flows in the period in which the unfavorable outcome occurs or becomes probable, and potentially in future periods.

Segment Information

6 Months Ended

Jul. 01, 2018

Segment Reporting [Abstract]

Segment Information

We have two reportable segments: Core Illumina and one segment related to the combined activities of our Consolidated VIEs. Our Consolidated VIEs currently include only the operations of Helix, whereas prior to the deconsolidation of GRAIL on February 28, 2017, our Consolidated VIEs included the combined operations of GRAIL and Helix.

We report segment information based on the management approach. This approach designates the internal reporting used by the Chief Operating Decision Maker (“CODM”) for making decisions and assessing performance as the source of our reportable segments. The CODM allocates resources and assesses the performance of each operating segment using information about its revenue and income (loss) from operations. Based on the information used by the CODM, we have determined our reportable segments as follows:

Core Illumina:

Core Illumina’s products and services serve customers in the research, clinical and applied markets, and enable the adoption of a variety of genomic solutions. Core Illumina includes all operations, excluding the results of the consolidated VIEs.

Consolidated VIEs:

Helix: Helix was established to enable individuals to explore their genetic information by providing affordable sequencing and database services for consumers through third-party partners, driving the creation of an ecosystem of consumer applications.

GRAIL: GRAIL was created to develop a blood test for early-stage cancer detection. GRAIL was in the early stages of developing this test and as such, had no revenues through the date of deconsolidation.

Management evaluates the performance of our operating segments based upon income (loss) from operations. We do not allocate expenses between segments. Core Illumina sells products and provides services to GRAIL and Helix in accordance with contractual agreements between the entities.

The following table presents the operating performance of each reportable segment (in millions):



	Three Months Ended						Six Months Ended
	July 1, 2018			July 2, 2017			July 1, 2018			July 2, 2017
Revenue:
Core Illumina	$	829		$	664		$	1,612		$	1,262
Consolidated VIEs	3			2			6			3
Elimination of intersegment revenue	(2		)	(4		)	(6		)	(4		)
Consolidated revenue	$	830		$	662		$	1,612		$	1,261

Income (loss) from operations:
Core Illumina	$	246		$	160		$	484		$	244
Consolidated VIEs	(20		)	(16		)	(41		)	(50		)
Elimination of intersegment earnings	1			(1		)	2			1
Consolidated income from operations	$	227		$	143		$	445		$	195

The following table presents the total assets of each reportable segment (in millions):



	July 1, 2018			December 31, 2017
Core Illumina	$	5,760		$	5,223
Consolidated VIEs	199			45
Elimination of intersegment assets	(108		)	(11		)
Consolidated total assets	$	5,851		$	5,257

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jul. 01, 2018
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements.
Consolidation	The unaudited condensed consolidated financial statements include our accounts, our wholly-owned subsidiaries, majority-owned or controlled companies, and variable interest entities (VIEs) for which we are the primary beneficiary. All intercompany transactions and balances have been eliminated in consolidation. In management’s opinion, the accompanying financial statements reflect all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation of the results for the interim periods presented.
Variable Interest Entities	We evaluate our ownership, contractual, and other interests in entities that are not wholly-owned to determine if these entities are VIEs, and, if so, whether we are the primary beneficiary of the VIE. In determining whether we are the primary beneficiary of a VIE and therefore required to consolidate the VIE, a qualitative approach is applied that determines whether we have both (1) the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and (2) the obligation to absorb losses of, or the rights to receive benefits from, the VIE that could potentially be significant to that VIE. We continuously assess whether we are the primary beneficiary of a VIE, as changes to existing relationships or future transactions may result in the consolidation or deconsolidation of such VIE. During the six months ended July 1, 2018, our consolidated VIE, Helix, received additional cash contributions from us and third-party investors in exchange for voting equity interests in Helix. Therefore, we reassessed and concluded that Helix continued to be a variable interest entity and that we remained the primary beneficiary. During the periods presented, we have not provided any other financial or other support to our VIEs that we were not contractually required to provide.
Equity Method Investments	The equity method is used to account for investments in which we have the ability to exercise significant influence, but not control, over the investee. Such investments are recorded within other assets, and the share of net income or losses of equity investments is recognized on a one quarter lag in other income, net.
Redeemable Noncontrolling Interests	Noncontrolling interests represent the portion of equity (net assets) in Helix, our consolidated but not wholly-owned entity, that is neither directly nor indirectly attributable to us. Noncontrolling interests with embedded contingent redemption features, such as put rights, that are not solely within our control are considered redeemable noncontrolling interests. Redeemable noncontrolling interests are presented outside of stockholders’ equity on the condensed consolidated balance sheets.
Fiscal Year	Our fiscal year is the 52 or 53 weeks ending the Sunday closest to December 31, with quarters of 13 or 14 weeks ending the Sunday closest to March 31, June 30, September 30, and December 31.
Reclassifications	Certain prior period amounts have been reclassified to conform to the current period presentation.
Recently Adopted and Issued Accounting Pronouncements	In February 2016, the FASB issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). The new standard requires lessees to recognize most leases on their balance sheet as lease liabilities with corresponding right-of-use assets. ASU 2016-02 is effective for us beginning in the first quarter of 2019. Currently, the standard will be adopted on a modified retrospective transition basis for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The FASB has proposed an alternative method to adopt the lease standard by recognizing a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We plan to utilize this alternative adoption method, if finalized by the FASB. In order to adopt the new standard in the first quarter of fiscal 2019, we are currently designing and implementing changes to our systems, processes, policies, and controls for lease accounting. We expect to elect the standard’s package of practical expedients on adoption, which allows us to carry forward our historical assessment of whether existing agreements contain a lease and the classification of our existing lease agreements. We do not expect to elect the standard’s available hindsight practical expedient on adoption. While we continue to review our existing lease agreements and assess the effects of adoption, we believe the new standard will have a material effect on our consolidated financial statements and disclosures. We expect substantially all of our real-estate operating lease commitments will be recognized as lease liabilities with corresponding right-of-use assets upon adoption, resulting in a significant increase in the assets and liabilities on the consolidated balance sheet. We are currently evaluating the impact of Topic 842 on the consolidated financial statements as it relates to other aspects of our business. In June 2016, the FASB issued Accounting Standards Update (ASU) 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments, which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. The standard is effective for us beginning in the first quarter of 2020, with early adoption permitted. We are currently evaluating the expected impact of ASU 2016-13 on our consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). The new standard is based on the principle that revenue should be recognized in an amount that reflects the consideration to which we expect to be entitled in exchange for the transfer of promised goods or services. We adopted Topic 606 using the modified retrospective transition method. The cumulative effect of applying the new revenue standard to all incomplete contracts as of January 1, 2018 was not material and, therefore, did not result in an adjustment to retained earnings. There was no material difference to the condensed consolidated financial statements for the three and six months ended July 1, 2018 due to the adoption of Topic 606. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10), which requires equity investments (other than those accounted for under the equity method or those that result in consolidation) to be measured at fair value, with changes in fair value recognized in net income. This standard was effective for us beginning in the first quarter of 2018. Based on our elections, our strategic equity investments that do not have readily determinable fair values and do not qualify for the net asset value practical expedient for estimating fair value are measured at cost, less any impairments, plus or minus changes resulting from observable price changes in orderly transactions for identifiable or similar investments of the same issuer. The measurement alternative was applied prospectively and did not result in an adjustment to retained earnings.
Revenue	Our revenue is generated primarily from the sale of products and services. Product revenue primarily consists of sales of instruments and consumables used in genetic analysis. Service and other revenue primarily consists of revenue generated from genotyping and sequencing services and instrument service contracts. We recognize revenue when control of our products and services is transferred to our customers in an amount that reflects the consideration we expect to receive from our customers in exchange for those products and services. This process involves identifying the contract with a customer, determining the performance obligations in the contract, determining the contract price, allocating the contract price to the distinct performance obligations in the contract, and recognizing revenue when the performance obligations have been satisfied. A performance obligation is considered distinct from other obligations in a contract when it provides a benefit to the customer either on its own or together with other resources that are readily available to the customer and is separately identified in the contract. We consider a performance obligation satisfied once we have transferred control of a good or service to the customer, meaning the customer has the ability to use and obtain the benefit of the good or service. We recognize revenue for satisfied performance obligations only when we determine there are no uncertainties regarding payment terms or transfer of control. Revenue from product sales is recognized generally upon delivery to the end customer, which is when control of the product is deemed to be transferred. Invoicing typically occurs upon shipment; the term between invoicing and when payment is due is not significant. In instances where right of payment or transfer of title is contingent upon the customer’s acceptance of the product, revenue is deferred until all acceptance criteria have been met. Revenue from instrument service contracts is recognized as the services are rendered, typically evenly over the contract term. Revenue from genotyping and sequencing services is recognized when earned, which is generally at the time the genotyping or sequencing analysis data is made available to the customer or agreed-upon milestones are reached. Revenue is recorded net of discounts, distributor commissions, and sales taxes collected on behalf of governmental authorities. Employee sales commissions are recorded as selling, general and administrative expenses when incurred as the amortization period for such costs, if capitalized, would have been one year or less. We regularly enter into contracts with multiple performance obligations. Such obligations are generally satisfied within a short time frame, approximately three to six months, after the contract execution date. Revenue recognition for contracts with multiple deliverables is based on the separate, distinct performance obligations within the contract. We do not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less, and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed. The contract price is allocated to each performance obligation in proportion to its standalone selling price. We determine our best estimate of standalone selling price using average selling prices over a rolling 12-month period coupled with an assessment of current market conditions. If the product or service has no history of sales or if the sales volume is not sufficient, we rely upon prices set by our pricing committee, adjusted for applicable discounts.
Earnings per Share	Basic earnings per share attributable to Illumina stockholders is computed based on the weighted average number of common shares outstanding during the period. Diluted earnings per share attributable to Illumina stockholders is computed based on the sum of the weighted average number of common shares and potentially dilutive common shares outstanding during the period. Per-share earnings of our VIEs are included in the consolidated basic and diluted earnings per share computations based on our share of the VIE’s securities. Potentially dilutive common shares consist of shares issuable under convertible senior notes and equity awards. Convertible senior notes have a dilutive impact when the average market price of our common stock exceeds the applicable conversion price of the respective notes. Potentially dilutive common shares from equity awards are determined using the average share price for each period under the treasury stock method. In addition, proceeds from exercise of equity awards and the average amount of unrecognized compensation expense for equity awards are assumed to be used to repurchase shares.
Strategic Investments	The carrying amounts of our strategic equity investments without readily determinable fair values are initially measured at cost and are remeasured for impairment and observable price changes in orderly transactions for identifiable or similar investments of the same issuer.
Intangible Assets and Goodwill	We test the carrying value of goodwill in accordance with accounting rules on impairment of goodwill, which require us to estimate the fair value of each reporting unit annually, or when impairment indicators exist, and compare such amounts to their respective carrying values to determine if an impairment is required.
Derivatives	We are exposed to foreign exchange rate risks in the normal course of business. We enter into foreign exchange contracts to manage foreign currency risks related to monetary assets and liabilities that are denominated in currencies other than the U.S. dollar. These foreign exchange contracts are carried at fair value in other current assets or accrued liabilities and are not designated as hedging instruments. Changes in the value of derivatives are recognized in other income, net, along with the remeasurement gain or loss on the foreign currency denominated assets or liabilities.
Warranties	We generally provide a one-year warranty on instruments. Additionally, we provide a warranty on consumables through the expiration date, which generally ranges from six to twelve months after the manufacture date. At the time revenue is recognized, an accrual is established for estimated warranty expenses based on historical experience as well as anticipated product performance. We periodically review the warranty reserve for adequacy and adjust the warranty accrual, if necessary, based on actual experience and estimated costs to be incurred. Warranty expense is recorded as a component of cost of product revenue.

Basis of Presentation and Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jul. 01, 2018

Accounting Policies [Abstract]

Disaggregation of Revenue from External Customers

The following tables represent revenue by source (in millions):



	Three Months Ended
	July 1, 2018						July 2, 2017
	Sequencing		Microarray		Total		Sequencing		Microarray		Total
Consumables	$	455	$	85	$	540	$	338	$	64	$	402
Instruments	123		4		127		130		6		136
Other product	6		—		6		5		—		5
Total product revenue	584		89		673		473		70		543
Service and other revenue	106		51		157		77		42		119
Total revenue	$	690	$	140	$	830	$	550	$	112	$	662



	Six Months Ended
	July 1, 2018						July 2, 2017
	Sequencing		Microarray		Total		Sequencing		Microarray		Total
Consumables	$	873	$	172	$	1,045	$	656	$	132	$	788
Instruments	235		9		244		225		11		236
Other product	11		1		12		9		1		10
Total product revenue	1,119		182		1,301		890		144		1,034
Service and other revenue	202		109		311		155		72		227
Total revenue	$	1,321	$	291	$	1,612	$	1,045	$	216	$	1,261

Revenue related to our Consolidated VIEs is included in sequencing services and other revenue.

The following table represents revenue by geographic area, based on region of destination (in millions):



	Three Months Ended				Six Months Ended
	July 1, 2018		July 2, 2017		July 1, 2018		July 2, 2017
United States	$	445	$	374	$	861	$	699
Europe	196		145		380		271
Greater China (1)	107		78		185		134
Asia-Pacific (1)	55		46		125		113
Other markets	27		19		61		44
Total revenue	$	830	$	662	$	1,612	$	1,261

____________________________________

(1) Revenue for the Greater China region, which consists of China, Taiwan, and Hong Kong, is reported separately from the Asia-Pacific region.

Summary of Calculation of Weighted Average Shares used to Calculate Basic and Diluted Earnings Per Share, Earnings Per Share

The following is the calculation of weighted average shares used to calculate basic and diluted earnings per share (in millions):



	Three Months Ended		Six Months Ended
	July 1, 2018	July 2, 2017	July 1, 2018	July 2, 2017
Weighted average shares outstanding	147	146	147	146
Effect of potentially dilutive common shares from:
Equity awards	1	1	1	1
Weighted average shares used in calculating diluted earnings per share	148	147	148	147

Balance Sheet Account Details (Tables)

6 Months Ended

Jul. 01, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Short-term Investments

The following is a summary of short-term investments (in millions):



	July 1, 2018							December 31, 2017
	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale debt securities:
Debt securities in government sponsored entities	$	25	$	—		$	25	$	67	$	—		$	67
Corporate debt securities	643		(1		)	642		423		(2		)	421
U.S. Treasury securities	504		(3		)	501		433		(1		)	432
Total available-for-sale debt securities	$	1,172	$	(4	)	$	1,168	$	923	$	(3	)	$	920

Summary of Contractual Maturities of Available-for-sale Debt Securities

Contractual maturities of available-for-sale debt securities as of July 1, 2018 were as follows (in millions):



	Estimated Fair Value
Due within one year	$	525
After one but within five years	643
Total	$	1,168

Summary of Inventory

Inventory consisted of the following (in millions):



	July 1, 2018		December 31, 2017
Raw materials	$	101	$	93
Work in process	212		188
Finished goods	49		52
Total inventory	$	362	$	333

Summary of Property and Equipment

Property and equipment, net consisted of the following (in millions):



	July 1, 2018			December 31, 2017
Leasehold improvements	$	483		$	331
Machinery and equipment	347			316
Computer hardware and software	214			185
Furniture and fixtures	41			34
Buildings	279			155
Construction in progress	148			326
Total property and equipment, gross	1,512			1,347
Accumulated depreciation	(476		)	(416		)
Total property and equipment, net	$	1,036		$	931

Summary of Changes in Goodwill

Changes to goodwill during the six months ended July 1, 2018 were as follows (in millions):



	Goodwill
Balance as of December 31, 2017	$	771
Current period acquisitions	60
Balance as of July 1, 2018	$	831

Summary of Accrued Liabilities

Accrued liabilities consisted of the following (in millions):



	July 1, 2018		December 31, 2017
Contract liabilities, current portion	$	168	$	150
Accrued compensation expenses	142		177
Accrued taxes payable	67		50
Other	45		55
Total accrued liabilities	$	422	$	432

Summary of Changes in Reserve for Product Warranties

Changes in the reserve for product warranties during the three and six months ended July 1, 2018 and July 2, 2017 were as follows (in millions):



	Three Months Ended						Six Months Ended
	July 1, 2018			July 2, 2017			July 1, 2018			July 2, 2017
Balance at beginning of period	$	16		$	12		$	17		$	13
Additions charged to cost of product revenue	6			7			12			11
Repairs and replacements	(7		)	(5		)	(14		)	(10		)
Balance at end of period	$	15		$	14		$	15		$	14

Summary of Activity of Redeemable Noncontrolling Interests

The activity of the redeemable noncontrolling interests during the six months ended July 1, 2018 was as follows (in millions):



	Redeemable Noncontrolling Interests
Balance as of December 31, 2017	$	220
Vesting of redeemable equity awards	1
Net loss attributable to noncontrolling interests	(17		)
Adjustment up to the redemption value	13
Balance as of July 1, 2018	$	217

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Fair Value Measurements (Tables)

6 Months Ended

Jul. 01, 2018

Fair Value Disclosures [Abstract]

Summary of Hierarchy for Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table presents the hierarchy for assets and liabilities measured at fair value on a recurring basis as of July 1, 2018 and December 31, 2017 (in millions):



	July 1, 2018								December 31, 2017
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Assets:
Money market funds (cash equivalents)	$	1,015	$	—	$	—	$	1,015	$	957	$	—	$	—	$	957
Debt securities in government-sponsored entities	—		25		—		25		—		67		—		67
Corporate debt securities	—		642		—		642		—		421		—		421
U.S. Treasury securities	501		—		—		501		432		—		—		432
Deferred compensation plan assets	—		37		—		37		—		35		—		35
Total assets measured at fair value	$	1,516	$	704	$	—	$	2,220	$	1,389	$	523	$	—	$	1,912
Liabilities:
Deferred compensation liability	$	—	$	35	$	—	$	35	$	—	$	33	$	—	$	33

Debt and Other Commitments (Tables)

6 Months Ended

Jul. 01, 2018

Debt Disclosure [Abstract]

Convertible Debt

Debt obligations consisted of the following (dollars in millions):



	July 1, 2018			December 31, 2017
Principal amount of 2019 Notes outstanding	$	633		$	633
Principal amount of 2021 Notes outstanding	517			517
Unamortized discount of liability component of convertible senior notes	(60		)	(75		)
Net carrying amount of liability component of convertible senior notes	1,090			1,075
Obligations under financing leases	254			113
Other	4			4
Less: current portion	(625		)	(10		)
Long-term debt	$	723		$	1,182
Carrying value of equity component of convertible senior notes, net of debt issuance cost	$	161		$	161
Fair value of convertible senior notes outstanding (Level 2)	$	1,427		$	1,305
Weighted-average remaining amortization period of discount on the liability component of convertible senior notes	2.4 years			2.8 years

Share-based Compensation Expense (Tables)

6 Months Ended

Jul. 01, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Share-based Compensation Expense for all Stock Awards

Share-based compensation expense reported in our statements of income was as follows (in millions):



	Three Months Ended						Six Months Ended
	July 1, 2018			July 2, 2017			July 1, 2018			July 2, 2017
Cost of product revenue	$	4		$	3		$	8		$	6
Cost of service and other revenue	1			1			2			1
Research and development	15			12			30			26
Selling, general and administrative	30			23			58			56
Share-based compensation expense before taxes	50			39			98			89
Related income tax benefits	(11		)	(12		)	(21		)	(23		)
Share-based compensation expense, net of taxes	$	39		$	27		$	77		$	66

Summary of Assumptions used to Estimate the Weighted-Average Fair Value Per Share for Stock Purchase under the Employee Stock Purchase Plan

The assumptions used for the specified reporting periods and the resulting estimates of weighted-average fair value per share for stock purchased under the Employee Stock Purchase Plan (ESPP) during the six months ended July 1, 2018 were as follows:



	Employee Stock Purchase Rights
Risk-free interest rate	1.22% - 1.89%
Expected volatility	29% - 39%
Expected term	0.5 - 1.0 year
Expected dividends	0		%
Weighted-average fair value per share	$	58.09

Stockholders' Equity (Tables)

6 Months Ended

Jul. 01, 2018

Equity [Abstract]

Summary of Restricted Stock Activity and Related Information, Restricted Stock

Restricted stock activity and related information for the six months ended July 1, 2018 was as follows (units in thousands):



	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		Weighted-Average Grant-Date Fair Value per Share
	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		RSU		PSU
Outstanding at December 31, 2017	2,085		542		$	172.92	$	166.15
Awarded	60		172		$	257.00	$	170.08
Vested	(103	)	—		$	159.10	—
Cancelled	(132	)	(20	)	$	169.22	$	163.78
Outstanding at July 1, 2018	1,910		694		$	176.56	$	167.19

______________________________________


(1)	The number of units reflect the estimated number of shares to be issued at the end of the performance period.

Summary of Restricted Stock Activity and Related Information, Performance Units

Restricted stock activity and related information for the six months ended July 1, 2018 was as follows (units in thousands):



	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		Weighted-Average Grant-Date Fair Value per Share
	Restricted Stock Units (RSU)		Performance Stock Units (PSU)(1)		RSU		PSU
Outstanding at December 31, 2017	2,085		542		$	172.92	$	166.15
Awarded	60		172		$	257.00	$	170.08
Vested	(103	)	—		$	159.10	—
Cancelled	(132	)	(20	)	$	169.22	$	163.78
Outstanding at July 1, 2018	1,910		694		$	176.56	$	167.19

______________________________________


(1)	The number of units reflect the estimated number of shares to be issued at the end of the performance period.

Summary of Stock Option Activity Under all Stock Option Plans

Stock option activity during the six months ended July 1, 2018 was as follows:



	Options (in thousands)		Weighted-Average Exercise Price
Outstanding at December 31, 2017	322		$	46.93
Exercised	(63	)	$	34.15
Outstanding and exercisable at July 1, 2018	259		$	50.01

Segment Information (Tables)

6 Months Ended

Jul. 01, 2018

Segment Reporting [Abstract]

Summary of Operating Performance and Assets by Segment

The following table presents the operating performance of each reportable segment (in millions):



	Three Months Ended						Six Months Ended
	July 1, 2018			July 2, 2017			July 1, 2018			July 2, 2017
Revenue:
Core Illumina	$	829		$	664		$	1,612		$	1,262
Consolidated VIEs	3			2			6			3
Elimination of intersegment revenue	(2		)	(4		)	(6		)	(4		)
Consolidated revenue	$	830		$	662		$	1,612		$	1,261

Income (loss) from operations:
Core Illumina	$	246		$	160		$	484		$	244
Consolidated VIEs	(20		)	(16		)	(41		)	(50		)
Elimination of intersegment earnings	1			(1		)	2			1
Consolidated income from operations	$	227		$	143		$	445		$	195

The following table presents the total assets of each reportable segment (in millions):



	July 1, 2018			December 31, 2017
Core Illumina	$	5,760		$	5,223
Consolidated VIEs	199			45
Elimination of intersegment assets	(108		)	(11		)
Consolidated total assets	$	5,851		$	5,257

Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jul. 01, 2018	Jul. 01, 2018	Dec. 31, 2017
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract liability	$ 196	$ 196	$ 181
Contract liabilities, current portion	168	168	$ 150
Revenue recognized, previously recorded as deferred revenue	$ 34	$ 102
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period		3 months
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period		6 months

Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Principles (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 830	$ 662	$ 1,612	$ 1,261
United States
Disaggregation of Revenue [Line Items]
Revenue	445	374	861	699
Europe
Disaggregation of Revenue [Line Items]
Revenue	196	145	380	271
Greater China
Disaggregation of Revenue [Line Items]
Revenue	107	78	185	134
Asia-Pacific
Disaggregation of Revenue [Line Items]
Revenue	55	46	125	113
Other markets
Disaggregation of Revenue [Line Items]
Revenue	27	19	61	44
Sequencing
Disaggregation of Revenue [Line Items]
Revenue	690	550	1,321	1,045
Microarray
Disaggregation of Revenue [Line Items]
Revenue	140	112	291	216
Consumables
Disaggregation of Revenue [Line Items]
Revenue	540	402	1,045	788
Consumables \| Sequencing
Disaggregation of Revenue [Line Items]
Revenue	455	338	873	656
Consumables \| Microarray
Disaggregation of Revenue [Line Items]
Revenue	85	64	172	132
Instruments
Disaggregation of Revenue [Line Items]
Revenue	127	136	244	236
Instruments \| Sequencing
Disaggregation of Revenue [Line Items]
Revenue	123	130	235	225
Instruments \| Microarray
Disaggregation of Revenue [Line Items]
Revenue	4	6	9	11
Other products
Disaggregation of Revenue [Line Items]
Revenue	6	5	12	10
Other products \| Sequencing
Disaggregation of Revenue [Line Items]
Revenue	6	5	11	9
Other products \| Microarray
Disaggregation of Revenue [Line Items]
Revenue			1	1
Total product revenue
Disaggregation of Revenue [Line Items]
Revenue	673	543	1,301	1,034
Total product revenue \| Sequencing
Disaggregation of Revenue [Line Items]
Revenue	584	473	1,119	890
Total product revenue \| Microarray
Disaggregation of Revenue [Line Items]
Revenue	89	70	182	144
Service and other revenue
Disaggregation of Revenue [Line Items]
Revenue	157	119	311	227
Service and other revenue \| Sequencing
Disaggregation of Revenue [Line Items]
Revenue	106	77	202	155
Service and other revenue \| Microarray
Disaggregation of Revenue [Line Items]
Revenue	$ 51	$ 42	$ 109	$ 72

Basis of Presentation and Summary of Significant Accounting Policies - Summary of Calculation of Weighted Average Shares used to Calculate Basic and Diluted Earnings Per Share (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Weighted average shares used to calculate basic and diluted earnings per share
Weighted average shares outstanding	147	146	147	146
Effect of potentially dilutive common shares from:
Equity awards	1	1	1	1
Weighted average shares used in calculating diluted earnings per share	148	147	148	147

Balance Sheet Account Details - Summary of Short-term Investments (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Available-for-sale debt securities:
Amortized Cost	$ 1,172	$ 923
Gross Unrealized Losses	(4)	(3)
Estimated Fair Value	1,168	920
Debt securities in government sponsored entities
Available-for-sale debt securities:
Amortized Cost	25	67
Gross Unrealized Losses
Estimated Fair Value	25	67
Corporate debt securities
Available-for-sale debt securities:
Amortized Cost	643	423
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	642	421
U.S. Treasury securities
Available-for-sale debt securities:
Amortized Cost	504	433
Gross Unrealized Losses	(3)	(1)
Estimated Fair Value	$ 501	$ 432

Balance Sheet Account Details - Summary of Contractual Maturities of Available-for-sale Debt Securities (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Estimated Fair Value
Due within one year	$ 525
After one but within five years	643
Total	$ 1,168	$ 920

Balance Sheet Account Details - Narrative - Strategic Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017	Dec. 31, 2017
Schedule of Investments [Line Items]
Commitment in new venture capital investment fund	$ 100		$ 100
Callable period			10 years
Remaining capital commitment	77		$ 77
Other Assets
Schedule of Investments [Line Items]
Strategic equity investments, without readily determinable fair values	263		263		$ 250
Equity method investments	21		21		$ 16
Investee
Schedule of Investments [Line Items]
Revenue from transactions with Company's cost-method investments in non-publicly traded companies	$ 36	$ 35	$ 72	$ 58

Balance Sheet Account Details - Summary of Inventory (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Raw materials	$ 101	$ 93
Work in process	212	188
Finished goods	49	52
Total inventory	$ 362	$ 333

Balance Sheet Account Details - Summary of Property and Equipment (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,512	$ 1,347
Accumulated depreciation	(476)	(416)
Total property and equipment, net	1,036	931
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	483	331
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	347	316
Computer hardware and software
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	214	185
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	41	34
Buildings
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	279	155
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 148	$ 326

Balance Sheet Account Details - Narrative - Property and Equipment (Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017
Property, Plant and Equipment [Line Items]
Non-cash expenditures included in capital expenditures	$ 42	$ 94
Construction In Progress And Build to Suit Lease Liability
Property, Plant and Equipment [Line Items]
Non-cash expenditures included in capital expenditures	$ 16	$ 60

Balance Sheet Account Details - Narrative - Intangible Assets and Goodwill (Details) - USD ($) $ in Millions		6 Months Ended
	May 14, 2018	Jul. 02, 2017
Finite-Lived Intangible Assets [Line Items]
Impairment of in-process research and development		$ 5
Cost of Sales
Finite-Lived Intangible Assets [Line Items]
Impairment of finite-lived intangible assets		$ 18
Edico Genome
Finite-Lived Intangible Assets [Line Items]
Cash consideration, net of cash acquired	$ 100
Goodwill, acquired during period	56
Developed technology \| Edico Genome
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired	$ 45
Useful life	10 years
Trade Name \| Edico Genome
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired	$ 1
Useful life	3 years

Balance Sheet Account Details - Summary of Changes in Goodwill (Details) $ in Millions	6 Months Ended
	Jul. 01, 2018 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 771
Current period acquisitions	60
Ending balance	$ 831

Balance Sheet Account Details - Narrative - Derivatives (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Not Designated as Hedging Instrument \| Foreign Exchange Forward
Derivative [Line Items]
Derivative, notional amount	$ 95	$ 88

Balance Sheet Account Details - Summary of Accrued Liabilities (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Contract liabilities, current portion	$ 168	$ 150
Accrued compensation expenses	142	177
Accrued taxes payable	67	50
Other	45	55
Total accrued liabilities	$ 422	$ 432

Balance Sheet Account Details - Narrative - Warranties (Details)	6 Months Ended
	Jul. 01, 2018
Instruments
Product Warranty Liability [Line Items]
Warranty period	1 year
Consumables \| Minimum
Product Warranty Liability [Line Items]
Warranty period	6 months
Consumables \| Maximum
Product Warranty Liability [Line Items]
Warranty period	12 months

Balance Sheet Account Details - Summary of Changes in Reserve for Product Warranties (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Reserve for product warranties [Roll Forward]
Balance at beginning of period	$ 16	$ 12	$ 17	$ 13
Additions charged to cost of product revenue	6	7	12	11
Repairs and replacements	(7)	(5)	(14)	(10)
Balance at end of period	$ 15	$ 14	$ 15	$ 14

Balance Sheet Account Details - Narrative - Investment in Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 01, 2018	Dec. 31, 2017	Jul. 02, 2017	Jan. 01, 2017	Jul. 31, 2015
Variable Interest Entity [Line Items]
Additional investment in exchange for voting equity interests	$ 100
Cash and cash equivalents	$ 1,344	$ 1,225	$ 1,219	$ 735
Helix Holdings I, LLC \| Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Equity ownership interest percentage	50.00%				50.00%
Ownership percentage by noncontrolling interest owners	50.00%
Cash and cash equivalents	$ 171

Balance Sheet Account Details - Narrative - Deconsolidation of GRAIL, Inc. (Details) - USD ($) $ in Millions		2 Months Ended	6 Months Ended
	Feb. 28, 2017	Feb. 28, 2017	Jul. 02, 2017	Jul. 01, 2018	Dec. 31, 2017	Feb. 27, 2017
Variable Interest Entity [Line Items]
Gain on deconsolidation of GRAIL			$ 453
GRAIL, Inc.
Variable Interest Entity [Line Items]
Cost-method investment ownership percentage	19.00%	19.00%
Cost-method investment voting interest percentage	13.00%	13.00%
Gain on deconsolidation of GRAIL	$ 453
GRAIL, Inc. \| Other Assets
Variable Interest Entity [Line Items]
Cost-method investments				$ 189	$ 185
Variable Interest Entity, Primary Beneficiary \| GRAIL, Inc.
Variable Interest Entity [Line Items]
Equity ownership interest percentage						52.00%
Percentage of GRAIL's losses absorbed		50.00%

Balance Sheet Account Details - Summary of Activity of Redeemable Noncontrolling Interests (Details) $ in Millions	6 Months Ended
	Jul. 01, 2018 USD ($)
Increase (Decrease) in Redeemable Noncontrolling Interests [Roll Forward]
Balance as of December 31, 2017	$ 220
Vesting of redeemable equity awards	1
Net loss attributable to noncontrolling interests	(17)
Adjustment up to the redemption value	13
Balance as of July 1, 2018	$ 217

Fair Value Measurements - Summary of Hierarchy for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Assets:
Available-for-sale securities	$ 1,168	$ 920
Debt securities in government sponsored entities
Assets:
Available-for-sale securities	25	67
Corporate debt securities
Assets:
Available-for-sale securities	642	421
U.S. Treasury securities
Assets:
Available-for-sale securities	501	432
Fair Value, Measurements, Recurring
Assets:
Deferred compensation plan assets	37	35
Total assets measured at fair value	2,220	1,912
Liabilities:
Deferred compensation liability	35	33
Fair Value, Measurements, Recurring \| Debt securities in government sponsored entities
Assets:
Available-for-sale securities	25	67
Fair Value, Measurements, Recurring \| Corporate debt securities
Assets:
Available-for-sale securities	642	421
Fair Value, Measurements, Recurring \| U.S. Treasury securities
Assets:
Available-for-sale securities	501	432
Fair Value, Measurements, Recurring \| Money market funds (cash equivalents)
Assets:
Money market funds (cash equivalents)	1,015	957
Fair Value, Measurements, Recurring \| Level 1
Assets:
Total assets measured at fair value	1,516	1,389
Fair Value, Measurements, Recurring \| Level 1 \| U.S. Treasury securities
Assets:
Available-for-sale securities	501	432
Fair Value, Measurements, Recurring \| Level 1 \| Money market funds (cash equivalents)
Assets:
Money market funds (cash equivalents)	1,015	957
Fair Value, Measurements, Recurring \| Level 2
Assets:
Deferred compensation plan assets	37	35
Total assets measured at fair value	704	523
Liabilities:
Deferred compensation liability	35	33
Fair Value, Measurements, Recurring \| Level 2 \| Debt securities in government sponsored entities
Assets:
Available-for-sale securities	25	67
Fair Value, Measurements, Recurring \| Level 2 \| Corporate debt securities
Assets:
Available-for-sale securities	$ 642	$ 421

Debt and Other Commitments - Summary of Information about Equity and Liability Components of Convertible Senior Notes Outstanding (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jul. 01, 2018	Dec. 31, 2017	Jun. 29, 2014
Debt Instrument [Line Items]
Obligations under financing leases	$ 254	$ 113
Other	4	4
Less: current portion	(625)	(10)
Long-term debt	723	1,182
Convertible Senior Notes
Debt Instrument [Line Items]
Unamortized discount of liability component of convertible senior notes	(60)	(75)
Net carrying amount of liability component of convertible senior notes	1,090	1,075
Carrying value of equity component, net of debt issuance cost	$ 161	$ 161
Weighted-average remaining amortization period of discount on the liability component of convertible senior notes	2 years 5 months	2 years 9 months
Level 2 \| Convertible Senior Notes
Debt Instrument [Line Items]
Fair value of convertible senior notes outstanding (Level 2)	$ 1,427	$ 1,305
2019 Notes \| Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount of notes outstanding	633	633	$ 633
2021 Notes \| Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount of notes outstanding	$ 517	$ 517	$ 517

Debt and Other Commitments - Narrative (Details) - Convertible Senior Notes $ / shares in Units, $ in Millions	1 Months Ended	6 Months Ended
	Jun. 29, 2014 USD ($) day $ / shares	Jul. 01, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)
2019 Notes
Debt Instrument [Line Items]
Stated rate		0.00%
Principal amount of notes outstanding \| $	$ 633	$ 633	$ 633
Effective interest rate used to measure fair value of converted notes upon conversion	2.90%
Conversion rate	0.0039318
Conversion price (in dollars per share) \| $ / shares	$ 254.34	$ 254.34
Threshold note trading days	5
Threshold consecutive note trading days	10
Threshold percentage of note price trigger	98.00%
Threshold common stock trading days	20
Threshold consecutive common stock trading days	30
Threshold percentage of common stock price trigger	130.00%
2021 Notes
Debt Instrument [Line Items]
Stated rate		0.50%
Principal amount of notes outstanding \| $	$ 517	$ 517	$ 517
Effective interest rate used to measure fair value of converted notes upon conversion	3.50%
Conversion rate	0.0039318
Conversion price (in dollars per share) \| $ / shares	$ 254.34	$ 254.34
Threshold note trading days	5
Threshold consecutive note trading days	10
Threshold percentage of note price trigger	98.00%
Threshold common stock trading days	20
Threshold consecutive common stock trading days	30
Threshold percentage of common stock price trigger	130.00%
Convertible Senior Notes Due 2019 and 2021
Debt Instrument [Line Items]
If-converted value in excess of principal \| $		$ 127

Debt and Other Commitments - Build-to-suit leases Narrative (Details) - USD ($) $ in Millions	Jul. 01, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Build-to-suit lease liability	$ 21	$ 144
Build-to-suit lease, asset under construction	21	144
Obligations under financing leases	254	$ 113
Construction In Progress And Build to Suit Lease Liability
Debt Instrument [Line Items]
Obligations under financing leases	$ 142

Share-based Compensation Expense - Summary of Share-based Compensation Expense for all Stock Awards (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense before taxes	$ 50	$ 39	$ 98	$ 89
Related income tax benefits	(11)	(12)	(21)	(23)
Share-based compensation expense, net of taxes	39	27	77	66
Cost of product revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense before taxes	4	3	8	6
Cost of service and other revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense before taxes	1	1	2	1
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense before taxes	15	12	30	26
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense before taxes	$ 30	$ 23	$ 58	$ 56

Share-based Compensation Expense - Summary of Assumptions used to Estimate the Weighted-Average Fair Value Per Share for Stock Purchase under the Employee Stock Purchase Plan (Details) - Employee Stock	6 Months Ended
	Jul. 01, 2018 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	29.00%
Expected volatility, maximum	39.00%
Expected dividends	0.00%
Weighted-average fair value per share (in dollars per share)	$ 58.09
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.22%
Expected term	6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.89%
Expected term	1 year

Share-based Compensation Expense - Narrative (Details) $ in Millions	6 Months Ended
	Jul. 01, 2018 USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Unrecognized compensation cost related to stock options, restricted stock, and ESPP shares granted to date	$ 328
Weighted-average period of unrecognized compensation cost related to stock options, restricted stock, and ESPP shares granted to date	2 years 4 months

Stockholders' Equity - Narrative (Details) shares in Millions	Jul. 01, 2018 shares
2015 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance (in shares)	5.5

Stockholders' Equity - Summary of Restricted Stock Activity and Related Information (Details) shares in Thousands	6 Months Ended
	Jul. 01, 2018 $ / shares shares
Restricted Stock Units (RSU)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at period start (in shares) \| shares	2,085
Awarded (in shares) \| shares	60
Vested (in shares) \| shares	(103)
Cancelled (in shares) \| shares	(132)
Outstanding at period end (in shares) \| shares	1,910
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Fair Value per Share, Outstanding at period start (in dollars per share) \| $ / shares	$ 172.92
Weighted-Average Grant Date Fair Value per Share, Awarded (in dollars per share) \| $ / shares	257.00
Weighted-Average Grant Date Fair Value per Share, Vested (in dollars per share) \| $ / shares	159.10
Weighted-Average Grant Date Fair Value per Share, Cancelled (in dollars per share) \| $ / shares	169.22
Weighted-Average Grant Date Fair Value per Share, Outstanding at period end (in dollars per share) \| $ / shares	$ 176.56
Performance Stock Units (PSU)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at period start (in shares) \| shares	542
Awarded (in shares) \| shares	172
Cancelled (in shares) \| shares	(20)
Outstanding at period end (in shares) \| shares	694
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Fair Value per Share, Outstanding at period start (in dollars per share) \| $ / shares	$ 166.15
Weighted-Average Grant Date Fair Value per Share, Awarded (in dollars per share) \| $ / shares	170.08
Weighted-Average Grant Date Fair Value per Share, Cancelled (in dollars per share) \| $ / shares	163.78
Weighted-Average Grant Date Fair Value per Share, Outstanding at period end (in dollars per share) \| $ / shares	$ 167.19

Stockholders' Equity - Summary of Stock Option Activity Under all Stock Option Plans (Details) shares in Thousands	6 Months Ended
	Jul. 01, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Outstanding at period start (in shares) \| shares	322
Options, Exercised (in shares) \| shares	(63)
Options, Outstanding at period end (in shares) \| shares	259
Options, Exercisable (in shares) \| shares	259
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Options, Outstanding at period start (in dollars per share) \| $ / shares	$ 46.93
Weighted-Average Exercise Price, Options, Exercised (in dollars per share) \| $ / shares	34.15
Weighted-Average Exercise Price, Options, Outstanding at period end (in dollars per share) \| $ / shares	50.01
Weighted-Average Exercise Price, Options, Exercisable (in dollars per share) \| $ / shares	$ 50.01

Stockholders' Equity - Narrative - Employee Stock Purchase Plan (Details) - ESPP - Employee Stock shares in Millions	6 Months Ended
	Jul. 01, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Specified percentage of the fair market value of the common stock on the first or last day of the offering period whichever is lower at which stock is purchased	85.00%
Total shares issued under the ESPP (in shares)	0.1
Shares available for issuance (in shares)	13.9

Stockholders' Equity - Narrative - Share Repurchases (Details) - USD ($) shares in Millions, $ in Millions	6 Months Ended	12 Months Ended
	Jul. 02, 2017	Dec. 31, 2017	Jul. 01, 2018	May 01, 2018	May 04, 2017	Jul. 28, 2016
Class of Stock [Line Items]
Common stock repurchases	$ 101
Common Stock
Class of Stock [Line Items]
Dollar amount remaining in authorized stock repurchase program			$ 250
Common Stock \| July 2016 Share Repurchase Plan
Class of Stock [Line Items]
Stock repurchase program, authorized amount						$ 250
Repurchase of common shares (in shares)		0.6
Common stock repurchases		$ 101
Common Stock \| May 2017 Share Repurchase Plan
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 250
Repurchase of common shares (in shares)		0.8
Common stock repurchases		$ 150
Common Stock \| May 2018 Share Repurchase Plan
Class of Stock [Line Items]
Stock repurchase program, authorized amount				$ 150

Income Taxes - Narrative (Details)	3 Months Ended	6 Months Ended
Income Taxes - Narrative (Details)	Jul. 01, 2018	Jul. 01, 2018
Income Tax Disclosure [Abstract]
Effective tax rate	13.90%	12.30%

Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
Segment Information (Details) $ in Millions	Jul. 01, 2018 USD ($)	Jul. 02, 2017 USD ($)	Jul. 01, 2018 USD ($) segment	Jul. 02, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment			2
Consolidated revenue	$ 830	$ 662	$ 1,612	$ 1,261
Consolidated income from operations	227	143	445	195
Consolidated total assets	5,851		5,851		$ 5,257
Operating Segments \| Core Illumina
Segment Reporting Information [Line Items]
Consolidated revenue	829	664	1,612	1,262
Consolidated income from operations	246	160	484	244
Consolidated total assets	5,760		5,760		5,223
Operating Segments \| Consolidated VIEs
Segment Reporting Information [Line Items]
Consolidated revenue	3	2	6	3
Consolidated income from operations	(20)	(16)	(41)	(50)
Consolidated total assets	199		199		45
Elimination of intersegment
Segment Reporting Information [Line Items]
Consolidated revenue	(2)	(4)	(6)	(4)
Consolidated income from operations	1	$ (1)	2	$ 1
Consolidated total assets	$ (108)		$ (108)		$ (11)