Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Nov. 02, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	JUNIPER NETWORKS INC
Entity Central Index Key	0001043604
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		345,154,400

Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Cost of revenues:
Total cost of revenues	468.8	485.4	1,436.2	1,466.8
Gross margin	711.0	772.4	2,030.3	2,320.9
Operating expenses:
Research and development	253.8	236.4	772.0	752.8
Sales and marketing	224.8	232.5	702.5	716.6
General and administrative	67.9	70.6	178.1	176.7
Restructuring charges	4.4	2.0	2.3	29.4
Total operating expenses	550.9	541.5	1,654.9	1,675.5
Operating income	160.1	230.9	375.4	645.4
Other expense, net	(8.1)	(5.1)	(31.1)	(33.8)
Income before income taxes	152.0	225.8	344.3	611.6
Income tax (benefit) provision	(71.8)	60.1	(30.4)	157.3
Net income	$ 223.8	$ 165.7	$ 374.7	$ 454.3
Net income per share:
Basic (in dollars per share)	$ 0.65	$ 0.44	$ 1.07	$ 1.20
Diluted, (in dollars per share)	$ 0.64	$ 0.43	$ 1.05	$ 1.18
Shares used in computing net income per share:
Basic (in shares)	346.2	378.3	350.1	380.0
Diluted (in shares)	350.5	382.7	355.2	386.5
Product
Total net revenues	$ 794.7	$ 869.7	$ 2,330.4	$ 2,615.8
Cost of revenues:
Total cost of revenues	312.5	336.0	955.5	1,026.4
Service
Total net revenues	385.1	388.1	1,136.1	1,171.9
Cost of revenues:
Total cost of revenues	$ 156.3	$ 149.4	$ 480.7	$ 440.4

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 223.8	$ 165.7	$ 374.7	$ 454.3
Available-for-sale debt securities:
Unrealized gains (losses) net of tax provision of $0.3 and benefit of $0.9 during the three and nine months ended September 30, 2018, respectively, and tax benefits of $0.5 and $0.2 for the corresponding periods of the fiscal year ended December 31, 2017 (fiscal 2017), respectively	0.9	(0.2)	(0.6)	1.4
Reclassification adjustment for realized net (losses) gains included in net income, net of tax provisions of zero for the three and nine months ended September 30, 2018, respectively, and net of tax provisions of $0.9 for each of the corresponding periods of fiscal 2017	0.0	(1.9)	0.9	(2.0)
Net change on available-for-sale debt securities, net of tax	0.9	(2.1)	0.3	(0.6)
Cash flow hedges:
Unrealized (losses) gains net of tax benefits of $1.5 and $2.7 during the three and nine months ended September 30, 2018, respectively, and net of tax provisions of $0.5 and $3.0 for the corresponding periods of fiscal 2017, respectively	(4.6)	6.3	(5.9)	14.6
Reclassification adjustment for realized net losses (gains) included in net income, net of tax benefit of $0.5 and provision of $0.3 during the three and nine months ended September 30, 2018, respectively, and net of tax provisions of $0.8 and $1.7 for the corresponding periods of fiscal 2017, respectively	2.6	(2.5)	(5.5)	(2.4)
Net change on cash flow hedges, net of tax	(2.0)	3.8	(11.4)	12.2
Change in foreign currency translation adjustments	(7.0)	8.4	(13.7)	19.3
Other comprehensive (loss) income, net of tax	(8.1)	10.1	(24.8)	30.9
Comprehensive income	$ 215.7	$ 175.8	$ 349.9	$ 485.2

Condensed Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on available-for-sale securities, tax (provision) benefit	$ (0.3)	$ 0.5	$ 0.9	$ 0.2
Reclassification adjustment for realized net loss (gain) on available-for-sale securities included in net income, tax provisions	0.0	0.9	0.0	0.9
Unrealized (loss) gain on cash flow hedges, tax (provision) benefit	1.5	(0.5)	2.7	(3.0)
Reclassification adjustment for realized net loss (gain) on cash flow hedges included in net income, tax provisions (benefit)	$ (0.5)	$ 0.8	$ 0.3	$ 1.7

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 2,501.7	$ 2,006.5
Short-term investments	887.3	1,026.1
Accounts receivable, net of allowances	648.3	852.0
Prepaid expenses and other current assets	253.4	299.9
Total current assets	4,290.7	4,184.5
Property and equipment, net	967.6	1,021.1
Long-term investments	259.0	988.4
Purchased intangible assets, net	115.0	128.1
Goodwill	3,094.3	3,096.2
Other long-term assets	373.7	415.5
Total assets	9,100.3	9,833.8
Current liabilities:
Accounts payable	184.7	217.6
Accrued compensation	177.2	186.0
Deferred revenue	814.1	1,030.3
Short-term debt	349.7	0.0
Other accrued liabilities	214.8	304.3
Total current liabilities	1,740.5	1,738.2
Long-term debt	1,788.6	2,136.3
Long-term deferred revenue	351.2	509.0
Long-term income taxes payable	436.7	650.6
Other long-term liabilities	132.4	118.8
Total liabilities	4,449.4	5,152.9
Commitments and contingencies (Note 13)
Stockholders' equity:
Convertible preferred stock, $0.00001 par value; 10.0 shares authorized; none issued and outstanding	0.0	0.0
Common stock, $0.00001 par value; 1,000.0 shares authorized; 345.1 shares and 365.5 shares issued and outstanding as of September 30, 2018 and December 31, 2017, respectively	0.0	0.0
Additional paid-in capital	7,698.4	8,042.1
Accumulated other comprehensive loss	(24.5)	(5.4)
Accumulated deficit	(3,023.0)	(3,355.8)
Total stockholders' equity	4,650.9	4,680.9
Total liabilities and stockholders' equity	$ 9,100.3	$ 9,833.8

Condensed Consolidated Balance Sheets (Parentheticals) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Convertible preferred stock - par value (in dollars per share)	$ 0.00001	$ 0.00001
Convertible preferred stock - shares authorized (shares)	10,000,000	10,000,000
Convertible preferred stock - issued (shares)	0	0
Convertible preferred stock - outstanding (shares)	0	0
Common stock - par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock - shares authorized (shares)	1,000,000,000	1,000,000,000
Common stock - issued (shares)	345,100,000	365,500,000
Common stock - outstanding (shares)	345,100,000	365,500,000

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 374.7	$ 454.3
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation expense	180.2	151.1
Depreciation, amortization, and accretion	159.2	169.7
Other	3.5	(6.7)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable, net	200.9	331.9
Prepaid expenses and other assets	43.9	51.2
Accounts payable	(27.6)	(11.5)
Accrued compensation	(4.2)	(60.6)
Income taxes payable	(244.0)	8.8
Other accrued liabilities	(14.5)	(20.3)
Deferred revenue	(23.4)	(21.2)
Net cash provided by operating activities	648.7	1,046.7
Cash flows from investing activities:
Purchases of property and equipment	(110.9)	(97.6)
Purchases of available-for-sale debt securities	(608.1)	(1,298.6)
Proceeds from sales of available-for-sale debt securities	1,012.2	761.2
Proceeds from maturities and redemptions of available-for-sale debt securities	446.6	521.3
Purchases of equity securities	(8.1)	(13.7)
Proceeds from sales of equity securities	29.8	1.3
Proceeds from Pulse note receivable	0.0	75.0
Payment of escrow balance related to prior year acquisitions	(31.5)	0.0
Payments for business acquisitions, net of cash and cash equivalents acquired	0.0	(27.0)
Net cash provided by (used in) investing activities	730.0	(78.1)
Cash flows from financing activities:
Repurchase and retirement of common stock	(755.5)	(395.5)
Proceeds from issuance of common stock	56.8	64.4
Payment of dividends	(187.0)	(113.5)
Change in customer financing arrangement	(16.9)	0.0
Other	(1.5)	0.0
Net cash used in financing activities	(904.1)	(444.6)
Effect of foreign currency exchange rates on cash, cash equivalents, and restricted cash	(10.9)	13.3
Net increase in cash, cash equivalents, and restricted cash	463.7	537.3
Cash, cash equivalents, and restricted cash at beginning of period	2,059.1	1,880.6
Cash, cash equivalents, and restricted cash at end of period	$ 2,522.8	$ 2,417.9

Basis of Presentation	9 Months Ended
Basis of Presentation	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Basis of Presentation The unaudited Condensed Consolidated Financial Statements of Juniper Networks, Inc. (the “Company” or “Juniper”) have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The Condensed Consolidated Balance Sheet as of December 31, 2017 has been derived from the audited Consolidated Financial Statements at that date. In the opinion of management, all adjustments, including normal recurring accruals, considered necessary for a fair presentation have been included. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018, or any future period. The information included in this Quarterly Report on Form 10-Q (“Report”) should be read in conjunction with “Management's Discussion and Analysis of Financial Condition and Results of Operations,” “Risk Factors,” “Quantitative and Qualitative Disclosures About Market Risk,” and the Consolidated Financial Statements and footnotes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "Form 10-K"). The Company adopted Financial Accounting Standards Board ("FASB") Accounting Standards Update ("ASU") No. 2016-18 (Topic 230) Statement of Cash Flow: Restricted Cash, effective January 1, 2018, using the retrospective transition method. Restricted cash of $47.4 million and $54.2 million has been included within cash, cash equivalents, and restricted cash when reconciling the beginning and ending total amounts, respectively, on the statement of cash flows for the nine months ended September 30, 2017, to conform to the current period presentation. The adoption did not have a material impact on the cash flow activity presented on the Company's Condensed Consolidated Statement of Cash Flows for the nine months ended September 30, 2017. See Note 3, Cash Equivalents and Investments, for a reconciliation of the cash balances within the Condensed Consolidated Statements of Cash Flows to the Condensed Consolidated Balance Sheets. The preparation of the financial statements and related disclosures in accordance with U.S. GAAP requires the Company to make judgments, assumptions, and estimates that affect the amounts reported in the Condensed Consolidated Financial Statements and the accompanying notes. Actual results could differ materially from those estimates under different assumptions or conditions.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Except for the change in certain policies upon adoption of the accounting standards described below, there have been no material changes to the Company's significant accounting policies, compared to the accounting policies described in Note 2, Significant Accounting Policies, in Notes to Consolidated Financial Statements in Item 8 of Part II of the Form 10-K.

Recently Adopted Accounting Standards

Comprehensive Income: Effective January 1, 2018, the Company early adopted FASB ASU No. 2018-02 (Topic 220), Income Statement - Reporting Comprehensive Income, issued in February 2018, with an election to reclassify stranded tax effects resulting from the U.S. Tax Cuts and Jobs Act (the "Tax Act"), from accumulated other comprehensive income to retained earnings. The adoption resulted in a reclassification of $5.7 million in income from accumulated other comprehensive loss to accumulated deficit as of the adoption date. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods.

Financial Instruments: On January 1, 2018, the Company adopted FASB ASU No. 2016-01, Financial Instruments—Overall: Recognition and Measurement of Financial Assets and Financial Liabilities and FASB ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall, which changes how entities classify and measure equity investments and present changes in the fair value of financial liabilities measured under the fair value option. The guidance also updates certain presentation and disclosure requirements. The Company adopted ASU 2016-01 as of January 1, 2018 using the modified retrospective method for its equity securities with readily determinable fair values and the prospective method for its equity securities without readily determinable fair values, resulting in no impact to the opening accumulated deficit balance. The Company has elected to use the measurement alternative for its equity investments without readily determinable fair value, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. See Note 3, Cash Equivalents and Investments for additional disclosures required upon adopting the standard.

Revenue Recognition: On January 1, 2018, the Company adopted FASB ASU No. 2014-09 (Topic 606) - Revenue from Contracts with Customers (“ASU 2014-09” or "Topic 606"), which provides guidance for revenue recognition that superseded the revenue recognition requirements in Accounting Standards Codification ("ASC") Topic 605, Revenue Recognition ("Topic 605") and most industry specific guidance. Under ASU 2014-09, revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. The Company adopted ASU 2014-09 under the modified retrospective approach, applying the amendments to prospective reporting periods. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with the historic accounting under Topic 605.

The cumulative effect of the changes made to the Company's Condensed Consolidated Balance Sheet as of January 1, 2018 for the adoption of Topic 606 to all contracts with customers that were not completed as of December 31, 2017 was recorded as an adjustment to accumulated deficit as of the adoption date as follows:



	December 31, 2017						January 1, 2018
	As reported			Adjustments			As adjusted
Assets:
Accounts receivable, net of allowances	$	852.0		$	(1.9	)	$	850.1
Prepaid expenses and other current assets	299.9			31.5			331.4
Other long-term assets	415.5			(21.1		)	394.4
Total assets	$	9,833.8		$	8.5		$	9,842.3

Liabilities:
Deferred revenue	$	1,030.3		$	(225.4	)	$	804.9
Other accrued liabilities	304.3			33.8			338.1
Long-term deferred revenue	509.0			(124.6		)	384.4
Total liabilities	$	5,152.9		$	(316.2	)	$	4,836.7

Stockholders' Equity:
Accumulated deficit	$	(3,355.8	)	$	324.7		$	(3,031.1	)

Upon adoption, the Company recorded a cumulative effect adjustment of $324.7 million, net of tax adjustment of $63.9 million, which decreased the January 1, 2018 opening accumulated deficit balance on the Condensed Consolidated Balance Sheet, primarily as a result of the following items:


•	Distributor Sales: Under Topic 606, the Company recognizes revenue from sales to distributors upon delivery of the product to the distributor, rather than upon delivery of the product to the end customer. Rebates and incentives offered to distributors, which are earned when sales to end customers are completed, are estimated at the point of revenue recognition.

•

Software Revenue: Under Topic 605, the Company deferred revenue for software licenses where vendor-specific objective evidence of fair value had not been established for undelivered items (primarily services). Under Topic 606, revenue for software licenses is recognized at the time of delivery unless the ongoing services provide frequent, critical updates to the software, without which the software functionality would be rapidly diminished.


•	Variable Consideration: Some of the Company's contracts include penalties, extended payment terms, acceptance provisions or other price variability that precluded revenue recognition under Topic 605 because of the requirement for amounts to be fixed or determinable. Topic 606 requires the Company to estimate and account for variable consideration as a reduction of the transaction price.

•

Revenue Allocation: Similar to Topic 605, Topic 606 requires an allocation of revenue between deliverables, or performance obligations, within an arrangement. Topic 605 restricted the allocation of revenue that is contingent on future deliverables to current deliverables; however, Topic 606 removes this restriction. In addition, the nature of the performance obligations identified within a contract under Topic 606 as compared to Topic 605 will impact the allocation of the transaction price between product and services.

•

Contract Acquisition Costs: Topic 606 requires the deferral and amortization of “incremental” costs incurred to obtain a contract where the associated contract duration is greater than one year. The primary contract acquisition cost for the Company are sales commissions. Prior to January 1, 2018, the Company expensed sales commissions. The change required by Topic 606 resulted in the creation of an asset on January 1, 2018.

The impact of adoption of Topic 606 on the Company's Condensed Consolidated Statements of Operations and Condensed Consolidated Balance Sheet was as follows (in millions):



	Three Months Ended September 30, 2018*							Nine Months Ended September 30, 2018*
	Three Months Ended September 30, 2018*							Nine Months Ended September 30, 2018*
	As Reported		Without Adoption of Topic 606		Topic 606 Impact			As Reported		Without Adoption of Topic 606		Topic 606 Impact
Net revenues:
Product	$	794.7	$	771.9	$	22.8		$	2,330.4	$	2,249.7	$	80.7
Service	385.1		412.5		(27.4		)	1,136.1		1,236.3		(100.2		)
Total net revenues	$	1,179.8	$	1,184.4	$	(4.6	)	$	3,466.5	$	3,486.0	$	(19.5	)

Operating expenses:
Sales and marketing	$	224.8	$	225.4	$	(0.6	)	$	702.5	$	697.6	$	4.9

________________________________


^*	Except as disclosed, the adoption of Topic 606 did not have a material impact on the Company’s Condensed Consolidated Statements of Operations for the three and nine months ended September 30, 2018.



	As of September 30, 2018
	As reported			Without Adoption of Topic 606			Topic 606 Impact
Assets:
Accounts receivable, net of allowances	$	648.3		$	635.3		$	13.0
Prepaid expenses and other current assets	253.4			232.6			20.8
Other long-term assets	373.7			371.8			1.9
Total assets	$	9,100.3		$	9,064.6		$	35.7

Liabilities:
Deferred revenue	$	814.1		$	1,044.7		$	(230.6	)
Other accrued liabilities	214.8			161.2			53.6
Long-term deferred revenue	351.2			445.5			(94.3		)
Total liabilities	$	4,449.4		$	4,720.7		$	(271.3	)

Stockholders' Equity:
Accumulated deficit	$	(3,023.0	)	$	(3,330.2	)	$	307.2

Revenue Recognition

Revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services by following a five-step process, (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price, and (5) recognize revenue when or as the Company satisfies a performance obligation, as further described below.

Identify the contract with a customer. The Company generally considers a sales contract or agreement with an approved purchase order as a customer contract provided that collection is considered probable, which is assessed based on the creditworthiness of the customer as determined by credit checks, payment histories, and/or other circumstances. The Company combines contracts with a customer if contracts are negotiated with a single commercial substance or contain price dependencies.

Identify the performance obligations in the contract. Product performance obligations include hardware and software licenses and service performance obligations include maintenance, software post-contract support, training, and professional services. Certain software licenses and related post-contract support are combined into a single performance obligation when the maintenance updates are critical to the continued functionality of the software.

Determine the transaction price. The transaction price for the Company’s contracts with its customers consists of both fixed and variable consideration provided it is probable that a significant reversal of revenue will not occur when the uncertainty related to variable consideration is resolved. Fixed consideration includes amounts to be contractually billed to the customer while variable consideration includes estimates for rights of return, rebates, and price protection, which are based on historical sales returns and price protection credits, specific criteria outlined in rebate agreements, and other factors known at the time. The Company generally invoices customers for hardware, software licenses and related maintenance arrangements at time of delivery, and professional services either upfront or upon meeting certain milestones. Customer invoices are generally due within 30 to 90 days after issuance. The Company’s contracts with customers typically do not include significant financing components as the period between the transfer of performance obligations and timing of payment are generally within one year.

Allocate the transaction price to the performance obligations in the contract. For contracts that contain multiple performance obligations, the Company allocates the transaction price to the performance obligations on a relative standalone selling price basis. Standalone selling prices are based on multiple factors including, but not limited to historical discounting trends for products and services, pricing practices in different geographies and through different sales channels, gross margin objectives, internal costs, competitor pricing strategies, and industry technology lifecycles.

Recognize revenue when or as the Company satisfies a performance obligation. Revenue for hardware and certain software licenses, are recognized at a point in time, which is generally upon shipment or delivery. Certain software licenses combined with post-contract support are recognized over time on a ratable basis over the term of the license. Revenue for maintenance and software post-contract support is recognized over time on a ratable basis over the contract term. Revenue from training and professional services is recognized over time as services are completed or ratably over the contractual period of generally one year or less.

Deferred Commissions

Sales commissions earned by the Company’s sales force are considered incremental and recoverable costs of obtaining a contract with a customer. These costs are deferred and then amortized over a period of benefit which is typically over the term of the customer contracts as initial commission rates and renewal rates are the same. Amortization expense is included in sales and marketing expenses in the accompanying Condensed Consolidated Statements of Operations.

Recent Accounting Standards Not Yet Adopted

Cloud Computing Arrangement: In August 2018, the FASB issued ASU No. 2018-15 (Subtopic 350-40) Intangibles-Goodwill and Other-Internal-Use Software: Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which provides guidance on a customer's accounting for implementation, set-up, and other upfront costs incurred in a cloud computing arrangement that is hosted by a service contract. The new standard is to be applied on either a retrospective or prospective basis to all implementation costs incurred after the date of adoption. The standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Fair Value Measurement: In August 2018, the FASB issued ASU No. 2018-13 (Topic 820) Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds, and modifies certain disclosure requirements for fair value measurements under ASC 820. This ASU is to be applied on a prospective basis for certain modified or new disclosure requirements, and all other amendments in the standard are to be applied on a retrospective basis. The new standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Derivatives and Hedging: In August 2017, the FASB issued ASU No. 2017-12 (Topic 815) Derivatives and Hedging — Targeted Improvements to Accounting for Hedging Activities, which expands an entity's ability to hedge financial and nonfinancial risk components and amends how companies assess effectiveness as well as changes the presentation and disclosure requirements. The new standard is to be applied on a modified retrospective basis and presentation and disclosure requirements will be applied on a prospective basis. This standard is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Amortization on Purchased Callable Debt Securities: In March 2017, the FASB issued ASU No. 2017-08 Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities which shortens the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The ASU will not impact debt securities held at a discount. This standard is effective for annual reporting periods beginning after December 15, 2018, including interim reporting periods within those annual reporting periods, and is to be applied on a modified retrospective basis with early adoption permitted. The adoption of this standard will not have an impact on the Consolidated Financial Statements.

Simplifying the Test for Goodwill Impairment: In January 2017, the FASB issued ASU No. 2017-04 (Topic 350) Intangibles—Goodwill and Other: Simplifying the Test for Goodwill Impairment, which removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. Under the amended guidance, a goodwill impairment charge will now be recognized for the amount by which the carrying value of a reporting unit exceeds its fair value, not to exceed the carrying amount of goodwill. This ASU will be applied on a prospective basis and is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted for any impairment tests performed after January 1, 2017.

Credit Losses on Financial Instruments: In June 2016, the FASB issued ASU No. 2016-13 (Topic 326) Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments, which provides more decision-useful information about the expected credit losses on financial instruments and changes the loss impairment methodology. This pronouncement is effective for reporting periods beginning after December 15, 2019, and interim periods within those fiscal years, using a modified retrospective adoption method. Early adoption is permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Leases: In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases, and several amendments thereafter, which requires recognition of lease assets and lease liabilities on the balance sheet by lessees for leases classified as operating leases under current GAAP. This ASU must be applied on a modified retrospective basis and is effective for financial statements issued for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. The Company intends to adopt this standard effective January 1, 2019. The Company is on schedule to complete its evaluation of the impact to the financial statements, disclosures, processes, systems, and controls. The Company currently anticipates a material impact related to the recognition of lease assets and lease liabilities for previously unrecognized leases on its Consolidated Balance Sheets, and does not expect this standard will have a material impact on the Consolidated Statements of Operations.

Cash Equivalents and Investments

9 Months Ended

Sep. 30, 2018

Cash Equivalents and Investments [Abstract]

Cash Equivalents and Investments

Investments in Available-for-Sale Debt Securities

The following table summarizes the Company's unrealized gains and losses and fair value of investments designated as available-for-sale debt securities as of September 30, 2018 and December 31, 2017 (in millions):



	As of September 30, 2018									As of December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Fixed income securities:
Asset-backed securities	$	71.9	$	—	$	(0.4	)	$	71.5	$	287.1	$	—	$	(0.6	)	$	286.5
Certificates of deposit	96.7		—		—			96.7		83.8		—		—			83.8
Commercial paper	334.7		—		—			334.7		217.1		—		—			217.1
Corporate debt securities	450.4		—		(3.7		)	446.7		929.6		0.4		(3.0		)	927.0
Foreign government debt securities	23.0		—		(0.2		)	22.8		62.9		—		(0.2		)	62.7
Time deposits	309.3		—		—			309.3		239.2		—		—			239.2
U.S. government agency securities	101.8		—		(0.3		)	101.5		143.9		—		(0.7		)	143.2
U.S. government securities	731.1		—		(0.8		)	730.3		406.8		0.1		(0.9		)	406.0
Total fixed income securities	2,118.9		—		(5.4		)	2,113.5		2,370.4		0.5		(5.4		)	2,365.5
Privately-held debt and redeemable preferred stock securities	16.6		37.4		—			54.0		15.9		37.4		—			53.3
Total available-for-sale debt securities	$	2,135.5	$	37.4	$	(5.4	)	$	2,167.5	$	2,386.3	$	37.9	$	(5.4	)	$	2,418.8

Reported as:
Cash equivalents	$	967.2	$	—	$	—		$	967.2	$	351.0	$	—	$	—		$	351.0
Short-term investments	889.5		—		(2.2		)	887.3		1,027.2		0.1		(1.2		)	1,026.1
Long-term investments	262.2		—		(3.2		)	259.0		992.2		0.4		(4.2		)	988.4
Other long-term assets	16.6		37.4		—			54.0		15.9		37.4		—			53.3
Total	$	2,135.5	$	37.4	$	(5.4	)	$	2,167.5	$	2,386.3	$	37.9	$	(5.4	)	$	2,418.8

The following table presents the contractual maturities of the Company's total fixed income securities as of September 30, 2018 (in millions):



	Amortized Cost		Estimated Fair Value
Due in less than one year	$	1,856.7	$	1,854.5
Due between one and five years	262.2		259.0
Total	$	2,118.9	$	2,113.5

The following tables present the Company's total fixed income securities that were in an unrealized loss position as of September 30, 2018 and December 31, 2017 (in millions):



	As of September 30, 2018
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Fixed income securities:
Asset-backed securities	$	16.9	$	(0.1	)	$	46.5	$	(0.3	)	$	63.4	$	(0.4	)
Commercial paper	0.8		—			—		—			0.8		—
Corporate debt securities	279.0		(2.3		)	136.9		(1.4		)	415.9		(3.7		)
Foreign government debt securities	8.0		—			13.4		(0.2		)	21.4		(0.2		)
U.S. government agency securities	67.8		(0.1		)	33.6		(0.2		)	101.4		(0.3		)
U.S. government securities	616.9		(0.3		)	62.4		(0.5		)	679.3		(0.8		)
Total fixed income securities	$	989.4	$	(2.8	)	$	292.8	$	(2.6	)	$	1,282.2	$	(5.4	)



	As of December 31, 2017
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Fixed income securities:
Asset-backed securities	$	215.2	$	(0.4	)	$	38.4	$	(0.2	)	$	253.6	$	(0.6	)
Corporate debt securities	646.7		(2.1		)	108.6		(0.9		)	755.3		(3.0		)
Foreign government debt securities	47.3		(0.2		)	6.6		—			53.9		(0.2		)
U.S. government agency securities	68.3		(0.2		)	67.9		(0.5		)	136.2		(0.7		)
U.S. government securities	260.8		(0.7		)	51.8		(0.2		)	312.6		(0.9		)
Total fixed income securities	$	1,238.3	$	(3.6	)	$	273.3	$	(1.8	)	$	1,511.6	$	(5.4	)

For available-for-sale debt securities that have unrealized losses, the Company assesses impairment by evaluating various factors, including whether (i) it has the intention to sell any of these investments and (ii) whether it is more likely than not that it will be required to sell any of these investments before recovery of the entire amortized cost basis. As of September 30, 2018, the Company had 539 investments in unrealized loss positions. The gross unrealized losses related to these investments were primarily due to changes in market interest rates. The Company anticipates that it will recover the entire amortized cost basis of such available-for-sale debt securities and has determined that no other-than-temporary impairments associated with credit losses were required to be recognized during the three and nine months ended September 30, 2018 and September 30, 2017.

During the three and nine months ended September 30, 2018 and September 30, 2017, there were no material gross realized gains or losses from available-for-sale debt securities.

Investments in Equity Securities

The following table presents the Company's investments in equity securities as of September 30, 2018 and December 31, 2017 (in millions):



	As of
	September 30, 2018		December 31, 2017
Equity investments with readily determinable fair value
Money market funds⁽¹⁾	$	1,126.2	$	969.8
Mutual funds⁽²⁾	28.0		27.6
Equity investments without readily determinable fair value⁽³⁾	32.6		29.7
Total equity securities	$	1,186.8	$	1,027.1

Reported as:
Cash equivalents	$	1,114.6	$	928.0
Prepaid expenses and other current assets	11.5		36.3
Other long-term assets	60.7		62.8
Total	$	1,186.8	$	1,027.1

________________________________


⁽¹⁾	Prior to January 1, 2018, money market funds were classified as available-for-sale securities and accounted for at fair value with unrealized gains and losses recognized in accumulated other comprehensive income (loss). Realized gains or losses from sales or impairments were recognized in the Condensed Consolidated Statements of Operations.


⁽²⁾	Prior to January 1, 2018, mutual funds related to the Company's non-qualified deferred compensation ("NQDC") plan were classified as trading securities. Unrealized gains or losses were recognized in the Condensed Consolidated Statements of Operations.


⁽³⁾	Prior to January 1, 2018, certain investments in privately-held companies were accounted for at cost less impairment. Realized gains or losses from sales or impairments were recognized in the Condensed Consolidated Statements of Operations.

For the three and nine months ended September 30, 2018 and September 30, 2017, there were no material unrealized gains or losses recognized for equity investments.

Restricted Cash and Investments

The Company has restricted cash and investments for: (i) amounts held in escrow accounts, as required in connection with certain acquisitions completed primarily between 2014 and 2017; (ii) amounts held under the Company's short-term disability plan in California; and (iii) amounts under the NQDC plan for senior-level employees. Restricted investments are now designated as equity investments as described in Note 2, Summary of Significant Accounting Policies. As of September 30, 2018, the carrying value of restricted cash and investments was $60.7 million, of which $26.6 million was included in prepaid expenses and other current assets and $34.1 million was included in other long-term assets on the Condensed Consolidated Balance Sheet.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash included in the Condensed Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 (in millions):



	As of
	September 30, 2018		December 31, 2017
Cash and cash equivalents	$	2,501.7	$	2,006.5
Restricted cash included in Prepaid expenses and other current assets	15.1		49.6
Restricted cash included in Other long-term assets	6.0		3.0
Total cash, cash equivalents, and restricted cash	$	2,522.8	$	2,059.1

Fair Value Measurements

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table provides a summary of assets and liabilities measured at fair value on a recurring basis and as reported in the Condensed Consolidated Balance Sheets (in millions):



	Fair Value Measurements at September 30, 2018										Fair Value Measurements at December 31, 2017
	Quoted Prices in Active Markets For Identical Assets (Level 1)		Significant Other Observable Remaining Inputs (Level 2)			Significant Other Unobservable Remaining Inputs (Level 3)		Total			Quoted Prices in Active Markets For Identical Assets (Level 1)		Significant Other Observable Remaining Inputs (Level 2)			Significant Other Unobservable Remaining Inputs (Level 3)		Total
Assets:
Available-for-sale debt securities:
Asset-backed securities	$	—	$	71.5		$	—	$	71.5		$	—	$	286.5		$	—	$	286.5
Certificates of deposit	—		96.7			—		96.7			—		83.8			—		83.8
Commercial paper	—		334.7			—		334.7			—		217.1			—		217.1
Corporate debt securities	—		446.7			—		446.7			—		927.0			—		927.0
Foreign government debt securities	—		22.8			—		22.8			—		62.7			—		62.7
Time deposits	—		309.3			—		309.3			—		239.2			—		239.2
U.S. government agency securities	—		101.5			—		101.5			—		143.2			—		143.2
U.S. government securities	313.5		416.8			—		730.3			322.4		83.6			—		406.0
Privately-held debt and redeemable preferred stock securities	—		—			54.0		54.0			—		—			53.3		53.3
Total available-for-sale debt securities	313.5		1,800.0			54.0		2,167.5			322.4		2,043.1			53.3		2,418.8
Equity securities:
Money market funds⁽¹⁾	1,126.2		—			—		1,126.2			969.8		—			—		969.8
Mutual funds⁽²⁾	28.0		—			—		28.0			27.6		—			—		27.6
Total equity securities	1,154.2		—			—		1,154.2			997.4		—			—		997.4
Derivative assets:
Foreign exchange contracts	—		3.6			—		3.6			—		9.2			—		9.2
Total assets measured at fair value	$	1,467.7	$	1,803.6		$	54.0	$	3,325.3		$	1,319.8	$	2,052.3		$	53.3	$	3,425.4
Liabilities:
Derivative liabilities:
Foreign exchange contracts	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)
Total liabilities measured at fair value	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)

Total assets, reported as:
Cash equivalents	$	1,176.2	$	905.6		$	—	$	2,081.8		$	928.1	$	350.9		$	—	$	1,279.0
Short-term investments	229.4		657.9			—		887.3			247.5		778.6			—		1,026.1
Long-term investments	22.5		236.5			—		259.0			74.8		913.6			—		988.4
Prepaid expenses and other current assets	11.5		3.6			—		15.1			36.3		9.2			—		45.5
Other long-term assets	28.1		—			54.0		82.1			33.1		—			53.3		86.4
Total assets measured at fair value	$	1,467.7	$	1,803.6		$	54.0	$	3,325.3		$	1,319.8	$	2,052.3		$	53.3	$	3,425.4

Total liabilities, reported as:
Other accrued liabilities	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)
Total liabilities measured at fair value	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)

________________________________


⁽¹⁾	Balance includes $11.6 million and $16.8 million in restricted investments measured at fair value, related to the Company's acquisition-related escrows as of September 30, 2018 and December 31, 2017, respectively. The December 31, 2017 balance also includes $25.0 million related to the Company's Directors and Officers indemnification trust, which was subsequently terminated.


⁽²⁾	Balance relates to restricted investments measured at fair value related to the Company's NQDC plan.

The Company's Level 2 available-for-sale debt securities are priced using quoted market prices for similar instruments or non-binding market prices that are corroborated by observable market data. The Company uses inputs such as actual trade data, benchmark yields, broker/dealer quotes, or alternative pricing sources with reasonable levels of price transparency which are obtained from quoted market prices, independent pricing vendors, or other sources, to determine the ultimate fair value of these assets. The Company's derivative instruments are classified as Level 2, as they are not actively traded and are valued using pricing models that use observable market inputs. The Company's policy is to recognize asset or liability transfers among Level 1, Level 2, and Level 3 at the beginning of the quarter in which a change in circumstances resulted in a transfer. During the three and nine months ended September 30, 2018, the Company had no transfers between levels of the fair value hierarchy of its assets or liabilities measured at fair value.

All of the Company's privately-held debt and redeemable preferred stock securities are classified as Level 3 assets due to the lack of observable inputs to determine fair value. The Company estimates the fair value of its privately-held debt and redeemable preferred stock securities on a recurring basis using an analysis of the financial condition and near-term prospects of the investee, including recent financing activities and the investee's capital structure. During the three and nine months ended September 30, 2018, there were no significant activities related to privately-held debt and redeemable preferred stocks securities.

Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis

Certain of the Company's assets, including intangible assets and goodwill, are measured at fair value on a nonrecurring basis, when they are deemed to be other-than temporarily impaired. There were no impairment charges recognized during the three and nine months ended September 30, 2018.

Equity investments without readily determinable fair value are measured at fair value, when they are deemed to be impaired or when there is an adjustment from observable price changes. For the three and nine months ended September 30, 2018, there were no impairment charges or adjustments resulting from observable price changes for equity investments without readily determinable fair value.

As of September 30, 2018 and December 31, 2017, the Company had no liabilities required to be measured at fair value on a nonrecurring basis.

Assets and Liabilities Not Measured at Fair Value

The carrying amounts of the Company's accounts receivable, accounts payable, and other accrued liabilities approximate fair value due to their short maturities. As of September 30, 2018 and December 31, 2017, the estimated fair value of the Company's short-term and long-term debt in the Condensed Consolidated Balance Sheets was $2,168.4 million and $2,252.9 million, respectively, based on observable market inputs (Level 2). The carrying value of the promissory note issued to the Company in connection with the previously completed sale of Junos Pulse (the “Pulse Note”), along with the accumulated interest paid in kind, of $64.6 million and $61.2 million approximates its fair value as of September 30, 2018 and December 31, 2017, respectively. The Pulse Note is classified as a Level 3 asset due to the lack of observable inputs to determine fair value.

- 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

Derivative Instruments

9 Months Ended

Sep. 30, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments

The Company uses derivatives to partially offset its market exposure to fluctuations in certain foreign currencies and does not enter into derivatives for speculative or trading purposes.

The notional amount of the Company's foreign currency derivatives are summarized as follows (in millions):



	As of
	September 30, 2018		December 31, 2017
Cash flow hedges	$	609.5	$	521.1
Non-designated derivatives	141.4		108.3
Total	$	750.9	$	629.4

Cash Flow Hedges

The Company uses foreign currency forward contracts to hedge the Company's planned cost of revenues and operating expenses denominated in foreign currencies. These derivatives are designated as cash flow hedges. Execution of cash flow hedge derivatives typically occurs every month with maturities of eighteen months or less. As of September 30, 2018, an estimated $5.8 million of unrealized net loss within accumulated other comprehensive loss is expected to be reclassified into earnings within the next 12 months.

The Company recognized an unrealized loss of $6.1 million and $8.6 million in accumulated other comprehensive loss for the effective portion of its derivative instruments for the three and nine months ended September 30, 2018, respectively; and an unrealized gain of $6.8 million and $17.6 million for the comparable periods in fiscal 2017, respectively. The Company reclassified a loss of $3.1 million and a gain of $5.8 million out of accumulated other comprehensive loss to cost of revenues and operating expenses in the Condensed Consolidated Statements of Operations during the three and nine months ended September 30, 2018, respectively. The amounts reclassified out of accumulated other comprehensive loss to cost of revenues and operating expenses in the Condensed Consolidated Statements of Operations were not material during the three and nine months ended September 30, 2017.

The ineffective portion of the Company's derivative instruments recognized in its Condensed Consolidated Statements of Operations was not material during the three and nine months ended September 30, 2018 and September 30, 2017.

See Note 4, Fair Value Measurements, for the fair values of the Company's derivative instruments in the Condensed Consolidated Balance Sheets.

Non-Designated Derivatives

The Company also uses foreign currency forward contracts to mitigate variability in gains and losses generated from the remeasurement of certain monetary assets and liabilities denominated in foreign currencies. These foreign exchange forward contracts typically have maturities of approximately one to three months. The outstanding non-designated derivative instruments are carried at fair value. Changes in the fair value of these derivatives recorded in other expense, net within the Condensed Consolidated Statements of Operations were not material during the three and nine months ended September 30, 2018 and September 30, 2017.

Other Financial Information

9 Months Ended

Sep. 30, 2018

Other Financial Information [Abstract]

Other Financial Information

Inventory

Total inventory consisted of the following (in millions):



	As of
	September 30, 2018		December 31, 2017
Production and service materials	$	56.3	$	71.2
Finished goods	19.3		26.6
Inventory	$	75.6	$	97.8

Reported as:
Prepaid expenses and other current assets	$	74.1	$	93.8
Other long-term assets	1.5		4.0
Total	$	75.6	$	97.8

Warranties

Changes during the nine months ended September 30, 2018 in the Company’s warranty reserve as reported within other accrued liabilities in the Condensed Consolidated Balance Sheets were as follows (in millions):



Balance as of December 31, 2017	$	27.4
Provisions made during the period	22.0
Actual costs incurred during the period	(23.0		)
Balance as of September 30, 2018	$	26.4

Deferred Revenue

Details of the Company's deferred revenue, as reported in the Condensed Consolidated Balance Sheets, were as follows (in millions):



	As of
	September 30, 2018			December 31, 2017
Deferred product revenue:
Undelivered product commitments and other product deferrals	$	144.5		$	312.6
Distributor inventory and other sell-through items	—			68.1
Deferred gross product revenue	144.5			380.7
Deferred cost of product revenue	(10.9		)	(46.5		)
Deferred product revenue, net	133.6			334.2
Deferred service revenue	1,031.7			1,205.1
Total	$	1,165.3		$	1,539.3
Reported as:
Current	$	814.1		$	1,030.3
Long-term	351.2			509.0
Total	$	1,165.3		$	1,539.3

Revenue

See Note 10, Segments, for disaggregated revenue by product and service, customer vertical, and geographic region.

Product revenue of $21.1 million and $77.6 million included in deferred revenue at January 1, 2018 was recognized during the three and nine months ended September 30, 2018, respectively. Service revenue of $150.0 million and $581.3 million included in deferred revenue at January 1, 2018 was recognized during the three and nine months ended September 30, 2018, respectively.

The following table summarizes the transaction price for contracts that have not yet been recognized as revenue as of September 30, 2018 and when the Company expects to recognize the amounts as revenue (in millions):



	Revenue Recognition Expected by Period
	Total		Less than 1 year		1-3 years		More than 3 years
Product	$	144.5	$	119.5	$	22.1	$	2.9
Service	1,031.7		705.5		292.2		34.0
Total	$	1,176.2	$	825.0	$	314.3	$	36.9

Deferred Commissions

Deferred commissions were $26.9 million as of September 30, 2018. For the three and nine months ended September 30, 2018, amortization expense for the deferred commissions was $31.2 million and $109.4 million, respectively. There were no impairment charges recognized during the three and nine months ended September 30, 2018.

Other Expense, Net

Other expense, net, consisted of the following (in millions):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Interest income	$	18.9		$	14.7		$	49.8		$	37.1
Interest expense	(25.8		)	(25.3		)	(77.7		)	(75.6		)
(Loss) gain on investments, net	(1.9		)	4.7			(1.8		)	6.7
Other	0.7			0.8			(1.4		)	(2.0		)
Other expense, net	$	(8.1	)	$	(5.1	)	$	(31.1	)	$	(33.8	)

Restructuring Charges

9 Months Ended

Sep. 30, 2018

Restructuring and Related Activities [Abstract]

Restructuring Charges

2018 Restructuring Plan

During the third quarter of 2018, the Company initiated a restructuring plan (the "2018 Restructuring Plan") to realign its workforce as a result of organizational and leadership changes.

In connection with the 2018 Restructuring Plan, the Company recorded $4.9 million of severance costs to restructuring charges in the Condensed Consolidated Statements of Operations during the three and nine months ended September 30, 2018. Subsequent to September 30, 2018, the Company amended the 2018 Restructuring Plan to further implement certain organizational changes resulting in a realignment of its workforce. As a result, the Company expects to record severance charges of approximately $5.0 million related to headcount reductions in the fourth quarter of 2018 and the Company does not anticipate future charges under the 2018 Restructuring Plan.

2017 Restructuring Plan

During 2017, the Company initiated a restructuring plan (the “2017 Restructuring Plan”) to realign its workforce and increase operational efficiencies. The 2017 Restructuring Plan consisted of severance and contract termination costs that were recorded to restructuring charges in the Condensed Consolidated Statements of Operations. During the three and nine months ended September 30, 2018, the Company recorded insignificant favorable adjustments for changes in previous estimates. The 2017 Restructuring Plan is substantially complete.

Restructuring liabilities are reported within other accrued liabilities in the Condensed Consolidated Balance Sheets. The following table provides a summary of changes in the restructuring liabilities for the Company's 2018 and 2017 restructuring plans (in millions):



	December 31, 2017		Charges/ (Benefits)			Cash Payments			Other		September 30, 2018
Severance	$	17.7	$	3.3		$	(19.3	)	$	0.1	$	1.8
Contract terminations and other	2.3		(1.0		)	(1.3		)	—		—
Total	$	20.0	$	2.3		$	(20.6	)	$	0.1	$	1.8

The Company expects to pay the remaining restructuring liabilities by the end of the first quarter of 2019, at which time the Company would consider the 2018 Restructuring Plan to be substantially complete.

Equity

9 Months Ended

Sep. 30, 2018

Stockholders' Equity Note [Abstract]

Equity

Cash Dividends on Shares of Common Stock

The following table summarizes the Company’s cash dividends declared per common stock:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cash dividends declared per common stock	$	0.18	$	0.10	$	0.54	$	0.30

The Company paid cash dividends of $0.18 and $0.10 per share each quarter, totaling $187.0 million and $113.5 million, during the nine months ended September 30, 2018 and September 30, 2017, respectively. Any future dividends, and the establishment of record and payment dates, are subject to approval by the Board of Directors (the “Board”) of Juniper Networks or an authorized committee thereof. See Note 14, Subsequent Event, for discussion of the Company's dividend declaration subsequent to September 30, 2018.

Stock Repurchase Activities

In January 2018, the Board approved a $2.0 billion share repurchase program ("2018 Stock Repurchase Program"), including $750.0 million to be used pursuant to an accelerated share repurchase program. The 2018 Stock Repurchase Program replaces the previous authorization approved by the Board in 2014 ("2014 Stock Repurchase Program").

As part of the 2018 Stock Repurchase Program, in February 2018, the Company entered into an accelerated share repurchase program (the "ASR") with two financial institutions to repurchase $750.0 million of the Company's common stock. During the three months ended March 31, 2018, the Company made an up-front payment of $750.0 million pursuant to the ASR and received an initial 23.3 million shares of the Company's common stock, based on the market value of the Company's common stock on the date of the transaction. During the three months ended September 30, 2018, the ASR was completed and an additional 6.0 million shares were received from the financial institutions for a total repurchase of 29.3 million shares of the Company's common stock at a volume weighted average repurchase price, less an agreed upon discount, of $25.62 per share. The shares received with respect to the ASR were retired and accounted for as a reduction to stockholders' equity in the Condensed Consolidated Balance Sheets.

The following table summarizes the Company's stock repurchases and retirements under its stock repurchase programs (in millions, except per share amounts):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018 ⁽¹⁾		2017 ⁽²⁾		2018 ⁽¹⁾		2017 ⁽²⁾
Shares repurchased	6.0		5.0		29.3		13.5
Average price per share	$	25.62	$	28.16	$	25.62	$	28.85
Amount repurchased	$	—	$	140.0	$	750.0	$	390.0

________________________________

⁽¹⁾Shares repurchased under the 2018 Stock Repurchase Program. $750.0 million represents the full amount of the ASR for which 23.3 million shares were received initially during the first quarter of 2018, and an additional 6.0 million shares were received at final settlement during the third quarter of 2018.

⁽²⁾Shares repurchased under the 2014 Stock Repurchase Program.

As of September 30, 2018, there were $1.3 billion of authorized funds remaining under the 2018 Stock Repurchase Program.

Future share repurchases under the 2018 Stock Repurchase Program will be subject to a review of the circumstances at that time and will be made from time to time in private transactions or open market purchases as permitted by securities laws and other legal requirements. The Company's 2018 Stock Repurchase Program may be discontinued at any time.

Accumulated Other Comprehensive Loss, Net of Tax

The components of accumulated other comprehensive loss, net of related taxes, for the nine months ended September 30, 2018 were as follows (in millions):



	Unrealized Gains/Losses on Available-for- Sale Debt Securities⁽¹⁾			Unrealized Gains/Losses on Cash Flow Hedges⁽²⁾			Foreign Currency Translation Adjustments			Total
Balance as of December 31, 2017	$	19.0		$	6.0		$	(30.4	)	$	(5.4	)
Other comprehensive loss before reclassifications	(0.6		)	(5.9		)	(13.7		)	(20.2		)
Amount reclassified from accumulated other comprehensive loss	0.9			(5.5		)	—			(4.6		)
Other comprehensive income (loss), net	0.3			(11.4		)	(13.7		)	(24.8		)
Reclassification of tax effects upon adoption of ASU 2018-02	5.0			0.7			—			5.7
Balance as of September 30, 2018	$	24.3		$	(4.7	)	$	(44.1	)	$	(24.5	)

________________________________


⁽¹⁾	The reclassifications out of accumulated other comprehensive loss during the nine months ended September 30, 2018 for realized gains/losses on available-for-sale debt securities were included in other expense, net, in the Condensed Consolidated Statements of Operations and were not material.


⁽²⁾	The reclassifications out of accumulated other comprehensive loss during the nine months ended September 30, 2018 for realized gains/losses on cash flow hedges were included within cost of revenues, research and development, sales and marketing, and general and administrative in the Condensed Consolidated Statements of Operations and were not material individually.

Employee Benefit Plans

9 Months Ended

Sep. 30, 2018

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

Employee Benefit Plans

Equity Incentive Plans

The Company has stock-based compensation plans pursuant to which it has granted stock options, restricted stock units (“RSUs”), and performance share awards (“PSAs”). The Company also maintains its 2008 Employee Stock Purchase Plan (the “ESPP”) for all eligible employees.

As of September 30, 2018, 23.3 million and 8.7 million shares were available for future issuance under the Company's 2015 Equity Incentive Plan (the "2015 Plan") and the ESPP, respectively.

Stock Option Activities

The following table summarizes the Company’s stock option activity and related information as of and for the nine months ended September 30, 2018 (in millions, except for per share amounts and years):



	Outstanding Options
	Number of Shares		Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (In Years)	Aggregate Intrinsic Value
Balance as of December 31, 2017	0.9		$	34.41
Exercised	(0.1	)	4.20
Expired/Canceled	(0.7	)	40.34
Balance as of September 30, 2018	0.1		$	19.80	1.9	$	1.2

As of September 30, 2018:
Vested and expected-to-vest options	0.1		$	19.80	1.9	$	1.2
Exercisable options	0.1		$	22.24	1.0	$	0.8

Restricted Stock Unit and Performance Share Award Activities

The Company’s RSU and PSA activity and related information as of and for the nine months ended September 30, 2018 were as follows (in millions, except per share amounts and years):



	Outstanding RSUs and PSAs⁽⁴⁾
	Number of Shares		Weighted Average Grant-Date Fair Value per Share		Weighted Average Remaining Contractual Term (In Years)	Aggregate Intrinsic Value
Balance as of December 31, 2017	19.5		$	25.39
RSUs granted ⁽¹⁾⁽³⁾	6.5		25.36
PSAs granted⁽²⁾⁽³⁾	0.7		24.43
RSUs vested	(5.4	)	25.43
PSAs vested	(1.1	)	24.14
RSUs canceled	(1.5	)	26.34
PSAs canceled	(0.7	)	24.39
Balance as of September 30, 2018	18.0		$	25.37	1.1	$	538.8

________________________________

⁽¹⁾

Includes service-based and market-based RSUs. The number of shares subject to market-based condition represents the aggregate maximum number of shares that may be issued pursuant to the award over its full term. The aggregate number of shares subject to market-based condition that would be issued if market criteria determined by the Compensation Committee of the Board are achieved at target is 0.1 million shares. Depending on achievement of such performance goals, the range of shares that could be issued under these awards is zero to 0.3 million shares.

⁽²⁾

The number of shares subject to PSAs granted represents the aggregate maximum number of shares that may be issued pursuant to the award over its full term. The aggregate number of shares subject to these PSAs that would be issued if performance goals determined by the Compensation Committee of the Board are achieved at target is 0.4 million shares. Depending on achievement of such performance goals, the range of shares that could be issued under these awards is zero to 0.7 million shares.

⁽³⁾

The grant date fair value of RSUs and PSAs were reduced by the present value of dividends expected to be paid on the underlying shares of common stock during the requisite and derived service period as these awards are not entitled to receive dividends until vested. During the nine months ended September 30, 2018, the Company declared a quarterly cash dividend of $0.18 per share of common stock on January 30, 2018, May 2, 2018, and July 26, 2018.

⁽⁴⁾

2.0 million shares of PSAs were modified during the nine months ended September 30, 2018, which relate primarily to PSAs assumed by the Company in connection with acquisitions consummated in 2016. These awards are contingent upon the achievement of certain performance milestones. Compensation cost resulting from the modifications totaled $6.3 million to be recognized over the remaining terms of the modified awards.

Employee Stock Purchase Plan

The following table summarizes employee stock purchases through the ESPP (in millions, except per share amounts):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Shares purchased	1.2		1.2		2.5		2.7
Average exercise price per share	$	22.39	$	22.79	$	22.31	$	20.83

On November 6, 2017, the Company’s Compensation Committee amended and restated the ESPP to provide that the offering period that began on February 1, 2018 would be for 24 months with four 6-month purchase periods. A new 24-month offering period will commence every six months thereafter. The purchase price for the Company’s common stock under the ESPP is 85% of the lower of the fair market value of the shares at (1) the beginning of the applicable offering period or (2) the end of each 6-month purchase period during such offering period. The ESPP will continue in effect until February 25, 2028, unless terminated earlier under the provisions of the ESPP.

Share-Based Compensation Expense

Share-based compensation expense associated with stock options, RSUs, restricted stock awards ("RSAs"), PSAs, and the ESPP was recorded in the following cost and expense categories in the Condensed Consolidated Statements of Operations (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenues - Product	$	1.5	$	1.5	$	5.1	$	3.8
Cost of revenues - Service	4.5		3.9		14.2		13.5
Research and development	28.1		18.5		101.8		67.4
Sales and marketing	12.9		13.7		40.4		45.3
General and administrative	6.2		7.4		18.7		21.1
Total	$	53.2	$	45.0	$	180.2	$	151.1

The following table summarizes share-based compensation expense by award type (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Stock options	$	0.1	$	0.2	$	0.3	$	0.5
RSUs, RSAs, and PSAs	48.2		41.0		165.8		138.9
ESPP	4.9		3.8		14.1		11.7
Total	$	53.2	$	45.0	$	180.2	$	151.1

As of September 30, 2018, the total unrecognized compensation cost related to unvested share-based awards was $320.2 million to be recognized over a weighted-average period of 1.6 years.

Segments

9 Months Ended

Sep. 30, 2018

Segment Reporting [Abstract]

Segments

The Company operates in one reportable segment. The Company's chief executive officer, who is the chief operating decision maker, reviews financial information presented on a consolidated basis for purposes of allocating resources and evaluating financial performance, accompanied by disaggregated information about net revenues by product and service, customer vertical, and geographic region as presented below.

The following table presents net revenues by product and service (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Routing	$	496.4	$	585.8	$	1,395.1	$	1,679.9
Switching	221.1		212.6		705.9		730.2
Security	77.2		71.3		229.4		205.7
Total product	794.7		869.7		2,330.4		2,615.8

Total service	385.1		388.1		1,136.1		1,171.9
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

The following table presents net revenues by customer vertical (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cloud	$	250.0	$	344.9	$	798.1	$	1,056.1
Service Provider	543.6		576.9		1,546.8		1,707.8
Enterprise	386.2		336.0		1,121.6		1,023.8
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

The Company attributes revenues to geographic region based on the customer’s shipping address. The following table presents net revenues by geographic region (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Americas:
United States	$	597.1	$	668.8	$	1,754.2	$	2,076.0
Other	46.0		60.4		152.2		165.6
Total Americas	643.1		729.2		1,906.4		2,241.6
Europe, Middle East, and Africa	329.9		298.6		946.8		871.3
Asia Pacific	206.8		230.0		613.3		674.8
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

Income Taxes

9 Months Ended

Sep. 30, 2018

Income Tax Disclosure [Abstract]

Income Taxes

The following table provides details of income taxes (in millions, except percentages):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Income before income taxes	$	152.0		$	225.8		$	344.3		$	611.6
Income tax (benefit) provision	$	(71.8	)	$	60.1		$	(30.4	)	$	157.3
Effective tax (benefit) rate	(47.2		)%	26.6		%	(8.8		)%	25.7		%

The Company's effective tax rate during the three and nine months ended September 30, 2018 differs from the federal statutory rate of 21%, primarily due to the recognition of certain previously unrecognized tax benefits of $67.6 million, which includes interest of $8.4 million, a reduction of expected tax liabilities of $33.2 million, federal research and development credits and a favorable change in the forecasted geographic mix of earnings. The recognition of $67.6 million in previously unrecognized tax benefits is due to a lapse in the federal statute of limitations relative to fiscal years 2010 through 2014. The reduction of expected tax liabilities of $33.2 million is a result of filing a change in accounting method for the tax recognition of deferred product revenue in the U.S. to better align with the financial statement recognition of such revenue.

The Tax Act enacted on December 22, 2017 introduced significant changes to U.S. income tax law. Effective January 1, 2018, the Tax Act reduced the U.S. federal corporate income tax rate from 35% to 21% and created a minimum tax on foreign earnings.

Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, the Company made reasonable estimates of the effects and recorded provisional amounts in the financial statements as of December 31, 2017. While the Company believes it has largely completed its analysis and related impacts of the Tax Act, the Company expects further guidance from revenue and taxation authorities in the fourth quarter of 2018, particularly from state authorities, which may impact the tax effects. As a result, the Company may make adjustments to the provisional amounts which may materially impact its provision for income taxes from continuing operations in the period in which the adjustments are made. The Company will complete the accounting for the tax effects of the Tax Act in the fourth quarter of 2018.

The Tax Act also includes provisions to tax Global Intangible Low-Taxed Income (“GILTI”) of foreign subsidiaries in excess of a deemed return on their tangible assets. The Company anticipates further guidance in the form of tax regulations to be issued by the U.S. Treasury in the fourth quarter of 2018, regarding the utilization of foreign tax credits relative to GILTI. Due to the complexities of the new provisions and the anticipated regulations referenced above, the Company is continuing to evaluate how the provisions will be accounted for under U.S. GAAP. Pursuant to the Tax Act, corporations are allowed to make an accounting policy election to either (i) account for GILTI as a component of income tax expense in the period in which the corporation is subject to the rules (the “period cost method”), or (ii) account for GILTI in the corporation's measurement of deferred taxes (the “deferred method”). The Company has not currently elected a method and will do so after completing its analysis of the GILTI provisions of the Tax Act depending on the analysis of the Company’s global income. Therefore, the Company has not recorded any potential deferred tax effects related to GILTI in its financial statements and has not yet made an accounting policy election regarding whether to record deferred taxes on GILTI or use the period cost method. The Company has, however, included an estimate of the current GILTI impact in its annual effective tax rate for 2018. The Company expects to complete the accounting during the measurement period.

As of September 30, 2018, the total amount of gross unrecognized tax benefits was $205.0 million, of which $183.3 million, if recognized, would affect the effective tax rate.

The Company engages in continuous discussions and negotiations with tax authorities regarding tax matters in various jurisdictions. It is reasonably possible that the balance of unrecognized tax benefits could decrease up to $7.9 million within the next twelve months due to lapses of applicable statutes of limitations and the completion of tax review cycles in various tax jurisdictions.

Net Income Per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Income Per Share

Net Income per Share

The Company computed basic and diluted net income per share as follows (in millions, except per share amounts):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Numerator:
Net income	$	223.8	$	165.7	$	374.7	$	454.3
Denominator:
Weighted-average shares used to compute basic net income per share	346.2		378.3		350.1		380.0
Dilutive effect of employee stock awards	4.3		4.4		5.1		6.5
Weighted-average shares used to compute diluted net income per share	350.5		382.7		355.2		386.5
Net income per share
Basic	$	0.65	$	0.44	$	1.07	$	1.20
Diluted	$	0.64	$	0.43	$	1.05	$	1.18

Anti-dilutive shares	4.2		1.0		5.0		1.2

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Commitments Except for the items below, there have been no material changes to the Company's commitments compared to the commitments described in Note 16, Commitments and Contingencies, in Notes to Consolidated Financial Statements in Item 8 of Part II of the Form 10-K. Purchase Commitments with Contract Manufacturers and Suppliers In order to reduce manufacturing lead times and in the interest of having access to adequate component supply, the Company enters into agreements with contract manufacturers and certain suppliers to procure inventory based on the Company's requirements. A significant portion of the Company's purchase commitments arising from these agreements consists of firm and non-cancelable commitments. These purchase commitments totaled $610.9 million as of September 30, 2018. The Company establishes a liability in connection with purchase commitments related to quantities in excess of its demand forecasts or obsolete materials charges for components purchased by the contract manufacturers based on the Company’s demand forecast or customer orders. As of September 30, 2018, the Company had accrued $23.6 million based on its estimate of such charges. Guarantees The Company enters into agreements with customers that contain indemnification provisions relating to potential situations where claims could be alleged that the Company’s products solely, or in combination with other third party products, infringe the intellectual property rights of a third-party. As of September 30, 2018 and December 31, 2017, the Company recorded $12.0 million and $20.4 million, respectively, for such indemnification obligations in other accrued liabilities and other long-term liabilities on the Condensed Consolidated Balance Sheets. Legal Proceedings Investigations The Company previously disclosed that it has been the subject of investigations by the U.S. Securities and Exchange Commission ("SEC") and the U.S. Department of Justice ("DOJ") into possible violations by the Company of the U.S. Foreign Corrupt Practices Act ("FCPA"). In cooperation with these investigations, the Company and the Audit Committee of the Board of Directors, with the assistance of outside counsel and other independent advisors, conducted a thorough internal investigation. As a result of its internal investigation, the Company made significant improvements in its internal controls and carried out a number of disciplinary actions. In the fourth quarter of 2017, the DOJ notified the Company that the DOJ has closed its investigation related to these matters without taking any action against the Company. The Company is continuing to fully cooperate with the SEC’s ongoing investigation, and based on the Company’s recent communications with the Staff of the SEC, the Company believes that it is likely that the Staff of the SEC will seek to bring an enforcement action against the Company. The Company believes it is probable that it could incur a loss and has established an estimated legal reserve of $12.0 million related to the ongoing SEC investigation; however, as discussions are continuing, there can be no assurance as to the timing or the terms of any final resolution of this matter. Other Litigations and Investigations In addition to the investigations discussed above, the Company is involved in other investigations, disputes, litigations, and legal proceedings. The Company records an accrual for loss contingencies for legal proceedings when it believes that an unfavorable outcome is both (a) probable and (b) the amount or range of any possible loss is reasonably estimable. The Company intends to aggressively defend itself in these matters, and while there can be no assurances and the outcome of these matters is currently not determinable, the Company currently believes that none of these existing claims or proceedings are likely to have a material adverse effect on its financial position. Notwithstanding the foregoing, there are many uncertainties associated with any litigation and these matters or other third-party claims against the Company may cause the Company to incur costly litigation and/or substantial settlement charges. In addition, the resolution of any intellectual property litigation may require the Company to make royalty payments, which could adversely affect gross margins in future periods. If any of those events were to occur, the Company's business, financial condition, results of operations, and cash flows could be adversely affected. The actual liability in any such matters may be materially different from the Company's estimates, if any, which could result in the need to adjust the liability and record additional expenses.

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event Dividend Declaration On October 23, 2018, the Company announced that it had declared a cash dividend of $0.18 per share of common stock payable on December 26, 2018 to stockholders of record as of the close of business on December 5, 2018.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Basis of Presentation

The unaudited Condensed Consolidated Financial Statements of Juniper Networks, Inc. (the “Company” or “Juniper”) have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The Condensed Consolidated Balance Sheet as of December 31, 2017 has been derived from the audited Consolidated Financial Statements at that date. In the opinion of management, all adjustments, including normal recurring accruals, considered necessary for a fair presentation have been included. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018, or any future period.

The information included in this Quarterly Report on Form 10-Q (“Report”) should be read in conjunction with “Management's Discussion and Analysis of Financial Condition and Results of Operations,” “Risk Factors,” “Quantitative and Qualitative Disclosures About Market Risk,” and the Consolidated Financial Statements and footnotes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 (the "Form 10-K").

The Company adopted Financial Accounting Standards Board ("FASB") Accounting Standards Update ("ASU") No. 2016-18 (Topic 230) Statement of Cash Flow: Restricted Cash, effective January 1, 2018, using the retrospective transition method. Restricted cash of $47.4 million and $54.2 million has been included within cash, cash equivalents, and restricted cash when reconciling the beginning and ending total amounts, respectively, on the statement of cash flows for the nine months ended September 30, 2017, to conform to the current period presentation. The adoption did not have a material impact on the cash flow activity presented on the Company's Condensed Consolidated Statement of Cash Flows for the nine months ended September 30, 2017. See Note 3, Cash Equivalents and Investments, for a reconciliation of the cash balances within the Condensed Consolidated Statements of Cash Flows to the Condensed Consolidated Balance Sheets.

The preparation of the financial statements and related disclosures in accordance with U.S. GAAP requires the Company to make judgments, assumptions, and estimates that affect the amounts reported in the Condensed Consolidated Financial Statements and the accompanying notes. Actual results could differ materially from those estimates under different assumptions or conditions.

Recently Adopted Accounting Standards and Recent Accounting Standards Not Yet Adopted

Recently Adopted Accounting Standards

Comprehensive Income: Effective January 1, 2018, the Company early adopted FASB ASU No. 2018-02 (Topic 220), Income Statement - Reporting Comprehensive Income, issued in February 2018, with an election to reclassify stranded tax effects resulting from the U.S. Tax Cuts and Jobs Act (the "Tax Act"), from accumulated other comprehensive income to retained earnings. The adoption resulted in a reclassification of $5.7 million in income from accumulated other comprehensive loss to accumulated deficit as of the adoption date. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods.

Financial Instruments: On January 1, 2018, the Company adopted FASB ASU No. 2016-01, Financial Instruments—Overall: Recognition and Measurement of Financial Assets and Financial Liabilities and FASB ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments - Overall, which changes how entities classify and measure equity investments and present changes in the fair value of financial liabilities measured under the fair value option. The guidance also updates certain presentation and disclosure requirements. The Company adopted ASU 2016-01 as of January 1, 2018 using the modified retrospective method for its equity securities with readily determinable fair values and the prospective method for its equity securities without readily determinable fair values, resulting in no impact to the opening accumulated deficit balance. The Company has elected to use the measurement alternative for its equity investments without readily determinable fair value, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. See Note 3, Cash Equivalents and Investments for additional disclosures required upon adopting the standard.

Revenue Recognition: On January 1, 2018, the Company adopted FASB ASU No. 2014-09 (Topic 606) - Revenue from Contracts with Customers (“ASU 2014-09” or "Topic 606"), which provides guidance for revenue recognition that superseded the revenue recognition requirements in Accounting Standards Codification ("ASC") Topic 605, Revenue Recognition ("Topic 605") and most industry specific guidance. Under ASU 2014-09, revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. The Company adopted ASU 2014-09 under the modified retrospective approach, applying the amendments to prospective reporting periods. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with the historic accounting under Topic 605.

The cumulative effect of the changes made to the Company's Condensed Consolidated Balance Sheet as of January 1, 2018 for the adoption of Topic 606 to all contracts with customers that were not completed as of December 31, 2017 was recorded as an adjustment to accumulated deficit as of the adoption date as follows:



	December 31, 2017						January 1, 2018
	As reported			Adjustments			As adjusted
Assets:
Accounts receivable, net of allowances	$	852.0		$	(1.9	)	$	850.1
Prepaid expenses and other current assets	299.9			31.5			331.4
Other long-term assets	415.5			(21.1		)	394.4
Total assets	$	9,833.8		$	8.5		$	9,842.3

Liabilities:
Deferred revenue	$	1,030.3		$	(225.4	)	$	804.9
Other accrued liabilities	304.3			33.8			338.1
Long-term deferred revenue	509.0			(124.6		)	384.4
Total liabilities	$	5,152.9		$	(316.2	)	$	4,836.7

Stockholders' Equity:
Accumulated deficit	$	(3,355.8	)	$	324.7		$	(3,031.1	)

Upon adoption, the Company recorded a cumulative effect adjustment of $324.7 million, net of tax adjustment of $63.9 million, which decreased the January 1, 2018 opening accumulated deficit balance on the Condensed Consolidated Balance Sheet, primarily as a result of the following items:


•	Distributor Sales: Under Topic 606, the Company recognizes revenue from sales to distributors upon delivery of the product to the distributor, rather than upon delivery of the product to the end customer. Rebates and incentives offered to distributors, which are earned when sales to end customers are completed, are estimated at the point of revenue recognition.

•

Software Revenue: Under Topic 605, the Company deferred revenue for software licenses where vendor-specific objective evidence of fair value had not been established for undelivered items (primarily services). Under Topic 606, revenue for software licenses is recognized at the time of delivery unless the ongoing services provide frequent, critical updates to the software, without which the software functionality would be rapidly diminished.


•	Variable Consideration: Some of the Company's contracts include penalties, extended payment terms, acceptance provisions or other price variability that precluded revenue recognition under Topic 605 because of the requirement for amounts to be fixed or determinable. Topic 606 requires the Company to estimate and account for variable consideration as a reduction of the transaction price.

•

Revenue Allocation: Similar to Topic 605, Topic 606 requires an allocation of revenue between deliverables, or performance obligations, within an arrangement. Topic 605 restricted the allocation of revenue that is contingent on future deliverables to current deliverables; however, Topic 606 removes this restriction. In addition, the nature of the performance obligations identified within a contract under Topic 606 as compared to Topic 605 will impact the allocation of the transaction price between product and services.

•

Contract Acquisition Costs: Topic 606 requires the deferral and amortization of “incremental” costs incurred to obtain a contract where the associated contract duration is greater than one year. The primary contract acquisition cost for the Company are sales commissions. Prior to January 1, 2018, the Company expensed sales commissions. The change required by Topic 606 resulted in the creation of an asset on January 1, 2018.

The impact of adoption of Topic 606 on the Company's Condensed Consolidated Statements of Operations and Condensed Consolidated Balance Sheet was as follows (in millions):



	Three Months Ended September 30, 2018*							Nine Months Ended September 30, 2018*
	Three Months Ended September 30, 2018*							Nine Months Ended September 30, 2018*
	As Reported		Without Adoption of Topic 606		Topic 606 Impact			As Reported		Without Adoption of Topic 606		Topic 606 Impact
Net revenues:
Product	$	794.7	$	771.9	$	22.8		$	2,330.4	$	2,249.7	$	80.7
Service	385.1		412.5		(27.4		)	1,136.1		1,236.3		(100.2		)
Total net revenues	$	1,179.8	$	1,184.4	$	(4.6	)	$	3,466.5	$	3,486.0	$	(19.5	)

Operating expenses:
Sales and marketing	$	224.8	$	225.4	$	(0.6	)	$	702.5	$	697.6	$	4.9

________________________________


^*	Except as disclosed, the adoption of Topic 606 did not have a material impact on the Company’s Condensed Consolidated Statements of Operations for the three and nine months ended September 30, 2018.



	As of September 30, 2018
	As reported			Without Adoption of Topic 606			Topic 606 Impact
Assets:
Accounts receivable, net of allowances	$	648.3		$	635.3		$	13.0
Prepaid expenses and other current assets	253.4			232.6			20.8
Other long-term assets	373.7			371.8			1.9
Total assets	$	9,100.3		$	9,064.6		$	35.7

Liabilities:
Deferred revenue	$	814.1		$	1,044.7		$	(230.6	)
Other accrued liabilities	214.8			161.2			53.6
Long-term deferred revenue	351.2			445.5			(94.3		)
Total liabilities	$	4,449.4		$	4,720.7		$	(271.3	)

Stockholders' Equity:
Accumulated deficit	$	(3,023.0	)	$	(3,330.2	)	$	307.2

Revenue Recognition

Revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services by following a five-step process, (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price, and (5) recognize revenue when or as the Company satisfies a performance obligation, as further described below.

Identify the contract with a customer. The Company generally considers a sales contract or agreement with an approved purchase order as a customer contract provided that collection is considered probable, which is assessed based on the creditworthiness of the customer as determined by credit checks, payment histories, and/or other circumstances. The Company combines contracts with a customer if contracts are negotiated with a single commercial substance or contain price dependencies.

Identify the performance obligations in the contract. Product performance obligations include hardware and software licenses and service performance obligations include maintenance, software post-contract support, training, and professional services. Certain software licenses and related post-contract support are combined into a single performance obligation when the maintenance updates are critical to the continued functionality of the software.

Determine the transaction price. The transaction price for the Company’s contracts with its customers consists of both fixed and variable consideration provided it is probable that a significant reversal of revenue will not occur when the uncertainty related to variable consideration is resolved. Fixed consideration includes amounts to be contractually billed to the customer while variable consideration includes estimates for rights of return, rebates, and price protection, which are based on historical sales returns and price protection credits, specific criteria outlined in rebate agreements, and other factors known at the time. The Company generally invoices customers for hardware, software licenses and related maintenance arrangements at time of delivery, and professional services either upfront or upon meeting certain milestones. Customer invoices are generally due within 30 to 90 days after issuance. The Company’s contracts with customers typically do not include significant financing components as the period between the transfer of performance obligations and timing of payment are generally within one year.

Allocate the transaction price to the performance obligations in the contract. For contracts that contain multiple performance obligations, the Company allocates the transaction price to the performance obligations on a relative standalone selling price basis. Standalone selling prices are based on multiple factors including, but not limited to historical discounting trends for products and services, pricing practices in different geographies and through different sales channels, gross margin objectives, internal costs, competitor pricing strategies, and industry technology lifecycles.

Recognize revenue when or as the Company satisfies a performance obligation. Revenue for hardware and certain software licenses, are recognized at a point in time, which is generally upon shipment or delivery. Certain software licenses combined with post-contract support are recognized over time on a ratable basis over the term of the license. Revenue for maintenance and software post-contract support is recognized over time on a ratable basis over the contract term. Revenue from training and professional services is recognized over time as services are completed or ratably over the contractual period of generally one year or less.

Deferred Commissions

Sales commissions earned by the Company’s sales force are considered incremental and recoverable costs of obtaining a contract with a customer. These costs are deferred and then amortized over a period of benefit which is typically over the term of the customer contracts as initial commission rates and renewal rates are the same. Amortization expense is included in sales and marketing expenses in the accompanying Condensed Consolidated Statements of Operations.

Recent Accounting Standards Not Yet Adopted

Cloud Computing Arrangement: In August 2018, the FASB issued ASU No. 2018-15 (Subtopic 350-40) Intangibles-Goodwill and Other-Internal-Use Software: Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which provides guidance on a customer's accounting for implementation, set-up, and other upfront costs incurred in a cloud computing arrangement that is hosted by a service contract. The new standard is to be applied on either a retrospective or prospective basis to all implementation costs incurred after the date of adoption. The standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Fair Value Measurement: In August 2018, the FASB issued ASU No. 2018-13 (Topic 820) Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds, and modifies certain disclosure requirements for fair value measurements under ASC 820. This ASU is to be applied on a prospective basis for certain modified or new disclosure requirements, and all other amendments in the standard are to be applied on a retrospective basis. The new standard is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Derivatives and Hedging: In August 2017, the FASB issued ASU No. 2017-12 (Topic 815) Derivatives and Hedging — Targeted Improvements to Accounting for Hedging Activities, which expands an entity's ability to hedge financial and nonfinancial risk components and amends how companies assess effectiveness as well as changes the presentation and disclosure requirements. The new standard is to be applied on a modified retrospective basis and presentation and disclosure requirements will be applied on a prospective basis. This standard is effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Amortization on Purchased Callable Debt Securities: In March 2017, the FASB issued ASU No. 2017-08 Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities which shortens the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The ASU will not impact debt securities held at a discount. This standard is effective for annual reporting periods beginning after December 15, 2018, including interim reporting periods within those annual reporting periods, and is to be applied on a modified retrospective basis with early adoption permitted. The adoption of this standard will not have an impact on the Consolidated Financial Statements.

Simplifying the Test for Goodwill Impairment: In January 2017, the FASB issued ASU No. 2017-04 (Topic 350) Intangibles—Goodwill and Other: Simplifying the Test for Goodwill Impairment, which removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. Under the amended guidance, a goodwill impairment charge will now be recognized for the amount by which the carrying value of a reporting unit exceeds its fair value, not to exceed the carrying amount of goodwill. This ASU will be applied on a prospective basis and is effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted for any impairment tests performed after January 1, 2017.

Credit Losses on Financial Instruments: In June 2016, the FASB issued ASU No. 2016-13 (Topic 326) Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments, which provides more decision-useful information about the expected credit losses on financial instruments and changes the loss impairment methodology. This pronouncement is effective for reporting periods beginning after December 15, 2019, and interim periods within those fiscal years, using a modified retrospective adoption method. Early adoption is permitted. The Company is currently evaluating the impact of adoption on the Consolidated Financial Statements.

Leases: In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases, and several amendments thereafter, which requires recognition of lease assets and lease liabilities on the balance sheet by lessees for leases classified as operating leases under current GAAP. This ASU must be applied on a modified retrospective basis and is effective for financial statements issued for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. The Company intends to adopt this standard effective January 1, 2019. The Company is on schedule to complete its evaluation of the impact to the financial statements, disclosures, processes, systems, and controls. The Company currently anticipates a material impact related to the recognition of lease assets and lease liabilities for previously unrecognized leases on its Consolidated Balance Sheets, and does not expect this standard will have a material impact on the Consolidated Statements of Operations.

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Schedule of new accounting pronouncements and changes in accounting principles

The impact of adoption of Topic 606 on the Company's Condensed Consolidated Statements of Operations and Condensed Consolidated Balance Sheet was as follows (in millions):



	Three Months Ended September 30, 2018*							Nine Months Ended September 30, 2018*
	Three Months Ended September 30, 2018*							Nine Months Ended September 30, 2018*
	As Reported		Without Adoption of Topic 606		Topic 606 Impact			As Reported		Without Adoption of Topic 606		Topic 606 Impact
Net revenues:
Product	$	794.7	$	771.9	$	22.8		$	2,330.4	$	2,249.7	$	80.7
Service	385.1		412.5		(27.4		)	1,136.1		1,236.3		(100.2		)
Total net revenues	$	1,179.8	$	1,184.4	$	(4.6	)	$	3,466.5	$	3,486.0	$	(19.5	)

Operating expenses:
Sales and marketing	$	224.8	$	225.4	$	(0.6	)	$	702.5	$	697.6	$	4.9

________________________________


^*	Except as disclosed, the adoption of Topic 606 did not have a material impact on the Company’s Condensed Consolidated Statements of Operations for the three and nine months ended September 30, 2018.



	As of September 30, 2018
	As reported			Without Adoption of Topic 606			Topic 606 Impact
Assets:
Accounts receivable, net of allowances	$	648.3		$	635.3		$	13.0
Prepaid expenses and other current assets	253.4			232.6			20.8
Other long-term assets	373.7			371.8			1.9
Total assets	$	9,100.3		$	9,064.6		$	35.7

Liabilities:
Deferred revenue	$	814.1		$	1,044.7		$	(230.6	)
Other accrued liabilities	214.8			161.2			53.6
Long-term deferred revenue	351.2			445.5			(94.3		)
Total liabilities	$	4,449.4		$	4,720.7		$	(271.3	)

Stockholders' Equity:
Accumulated deficit	$	(3,023.0	)	$	(3,330.2	)	$	307.2

The cumulative effect of the changes made to the Company's Condensed Consolidated Balance Sheet as of January 1, 2018 for the adoption of Topic 606 to all contracts with customers that were not completed as of December 31, 2017 was recorded as an adjustment to accumulated deficit as of the adoption date as follows:



	December 31, 2017						January 1, 2018
	As reported			Adjustments			As adjusted
Assets:
Accounts receivable, net of allowances	$	852.0		$	(1.9	)	$	850.1
Prepaid expenses and other current assets	299.9			31.5			331.4
Other long-term assets	415.5			(21.1		)	394.4
Total assets	$	9,833.8		$	8.5		$	9,842.3

Liabilities:
Deferred revenue	$	1,030.3		$	(225.4	)	$	804.9
Other accrued liabilities	304.3			33.8			338.1
Long-term deferred revenue	509.0			(124.6		)	384.4
Total liabilities	$	5,152.9		$	(316.2	)	$	4,836.7

Stockholders' Equity:
Accumulated deficit	$	(3,355.8	)	$	324.7		$	(3,031.1	)

Cash Equivalents and Investments (Tables)

9 Months Ended

Sep. 30, 2018

Cash Equivalents and Investments [Abstract]

Unrealized gains and losses and fair value of available-for-sale debt securities

The following table summarizes the Company's unrealized gains and losses and fair value of investments designated as available-for-sale debt securities as of September 30, 2018 and December 31, 2017 (in millions):



	As of September 30, 2018									As of December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Fixed income securities:
Asset-backed securities	$	71.9	$	—	$	(0.4	)	$	71.5	$	287.1	$	—	$	(0.6	)	$	286.5
Certificates of deposit	96.7		—		—			96.7		83.8		—		—			83.8
Commercial paper	334.7		—		—			334.7		217.1		—		—			217.1
Corporate debt securities	450.4		—		(3.7		)	446.7		929.6		0.4		(3.0		)	927.0
Foreign government debt securities	23.0		—		(0.2		)	22.8		62.9		—		(0.2		)	62.7
Time deposits	309.3		—		—			309.3		239.2		—		—			239.2
U.S. government agency securities	101.8		—		(0.3		)	101.5		143.9		—		(0.7		)	143.2
U.S. government securities	731.1		—		(0.8		)	730.3		406.8		0.1		(0.9		)	406.0
Total fixed income securities	2,118.9		—		(5.4		)	2,113.5		2,370.4		0.5		(5.4		)	2,365.5
Privately-held debt and redeemable preferred stock securities	16.6		37.4		—			54.0		15.9		37.4		—			53.3
Total available-for-sale debt securities	$	2,135.5	$	37.4	$	(5.4	)	$	2,167.5	$	2,386.3	$	37.9	$	(5.4	)	$	2,418.8

Reported as:
Cash equivalents	$	967.2	$	—	$	—		$	967.2	$	351.0	$	—	$	—		$	351.0
Short-term investments	889.5		—		(2.2		)	887.3		1,027.2		0.1		(1.2		)	1,026.1
Long-term investments	262.2		—		(3.2		)	259.0		992.2		0.4		(4.2		)	988.4
Other long-term assets	16.6		37.4		—			54.0		15.9		37.4		—			53.3
Total	$	2,135.5	$	37.4	$	(5.4	)	$	2,167.5	$	2,386.3	$	37.9	$	(5.4	)	$	2,418.8

Maturities of fixed income securities

The following table presents the contractual maturities of the Company's total fixed income securities as of September 30, 2018 (in millions):



	Amortized Cost		Estimated Fair Value
Due in less than one year	$	1,856.7	$	1,854.5
Due between one and five years	262.2		259.0
Total	$	2,118.9	$	2,113.5

Available-for-sale securities in unrealized loss position

The following tables present the Company's total fixed income securities that were in an unrealized loss position as of September 30, 2018 and December 31, 2017 (in millions):



	As of September 30, 2018
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Fixed income securities:
Asset-backed securities	$	16.9	$	(0.1	)	$	46.5	$	(0.3	)	$	63.4	$	(0.4	)
Commercial paper	0.8		—			—		—			0.8		—
Corporate debt securities	279.0		(2.3		)	136.9		(1.4		)	415.9		(3.7		)
Foreign government debt securities	8.0		—			13.4		(0.2		)	21.4		(0.2		)
U.S. government agency securities	67.8		(0.1		)	33.6		(0.2		)	101.4		(0.3		)
U.S. government securities	616.9		(0.3		)	62.4		(0.5		)	679.3		(0.8		)
Total fixed income securities	$	989.4	$	(2.8	)	$	292.8	$	(2.6	)	$	1,282.2	$	(5.4	)



	As of December 31, 2017
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Fixed income securities:
Asset-backed securities	$	215.2	$	(0.4	)	$	38.4	$	(0.2	)	$	253.6	$	(0.6	)
Corporate debt securities	646.7		(2.1		)	108.6		(0.9		)	755.3		(3.0		)
Foreign government debt securities	47.3		(0.2		)	6.6		—			53.9		(0.2		)
U.S. government agency securities	68.3		(0.2		)	67.9		(0.5		)	136.2		(0.7		)
U.S. government securities	260.8		(0.7		)	51.8		(0.2		)	312.6		(0.9		)
Total fixed income securities	$	1,238.3	$	(3.6	)	$	273.3	$	(1.8	)	$	1,511.6	$	(5.4	)

Schedule of investments in equity securities

The following table presents the Company's investments in equity securities as of September 30, 2018 and December 31, 2017 (in millions):



	As of
	September 30, 2018		December 31, 2017
Equity investments with readily determinable fair value
Money market funds⁽¹⁾	$	1,126.2	$	969.8
Mutual funds⁽²⁾	28.0		27.6
Equity investments without readily determinable fair value⁽³⁾	32.6		29.7
Total equity securities	$	1,186.8	$	1,027.1

Reported as:
Cash equivalents	$	1,114.6	$	928.0
Prepaid expenses and other current assets	11.5		36.3
Other long-term assets	60.7		62.8
Total	$	1,186.8	$	1,027.1

________________________________


⁽¹⁾	Prior to January 1, 2018, money market funds were classified as available-for-sale securities and accounted for at fair value with unrealized gains and losses recognized in accumulated other comprehensive income (loss). Realized gains or losses from sales or impairments were recognized in the Condensed Consolidated Statements of Operations.


⁽²⁾	Prior to January 1, 2018, mutual funds related to the Company's non-qualified deferred compensation ("NQDC") plan were classified as trading securities. Unrealized gains or losses were recognized in the Condensed Consolidated Statements of Operations.


⁽³⁾	Prior to January 1, 2018, certain investments in privately-held companies were accounted for at cost less impairment. Realized gains or losses from sales or impairments were recognized in the Condensed Consolidated Statements of Operations.

Schedule of reconciliation of cash, cash equivalents and restricted cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash included in the Condensed Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 (in millions):



	As of
	September 30, 2018		December 31, 2017
Cash and cash equivalents	$	2,501.7	$	2,006.5
Restricted cash included in Prepaid expenses and other current assets	15.1		49.6
Restricted cash included in Other long-term assets	6.0		3.0
Total cash, cash equivalents, and restricted cash	$	2,522.8	$	2,059.1

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Assets and liabilities measured at fair value on a recurring basis

The following table provides a summary of assets and liabilities measured at fair value on a recurring basis and as reported in the Condensed Consolidated Balance Sheets (in millions):



	Fair Value Measurements at September 30, 2018										Fair Value Measurements at December 31, 2017
	Quoted Prices in Active Markets For Identical Assets (Level 1)		Significant Other Observable Remaining Inputs (Level 2)			Significant Other Unobservable Remaining Inputs (Level 3)		Total			Quoted Prices in Active Markets For Identical Assets (Level 1)		Significant Other Observable Remaining Inputs (Level 2)			Significant Other Unobservable Remaining Inputs (Level 3)		Total
Assets:
Available-for-sale debt securities:
Asset-backed securities	$	—	$	71.5		$	—	$	71.5		$	—	$	286.5		$	—	$	286.5
Certificates of deposit	—		96.7			—		96.7			—		83.8			—		83.8
Commercial paper	—		334.7			—		334.7			—		217.1			—		217.1
Corporate debt securities	—		446.7			—		446.7			—		927.0			—		927.0
Foreign government debt securities	—		22.8			—		22.8			—		62.7			—		62.7
Time deposits	—		309.3			—		309.3			—		239.2			—		239.2
U.S. government agency securities	—		101.5			—		101.5			—		143.2			—		143.2
U.S. government securities	313.5		416.8			—		730.3			322.4		83.6			—		406.0
Privately-held debt and redeemable preferred stock securities	—		—			54.0		54.0			—		—			53.3		53.3
Total available-for-sale debt securities	313.5		1,800.0			54.0		2,167.5			322.4		2,043.1			53.3		2,418.8
Equity securities:
Money market funds⁽¹⁾	1,126.2		—			—		1,126.2			969.8		—			—		969.8
Mutual funds⁽²⁾	28.0		—			—		28.0			27.6		—			—		27.6
Total equity securities	1,154.2		—			—		1,154.2			997.4		—			—		997.4
Derivative assets:
Foreign exchange contracts	—		3.6			—		3.6			—		9.2			—		9.2
Total assets measured at fair value	$	1,467.7	$	1,803.6		$	54.0	$	3,325.3		$	1,319.8	$	2,052.3		$	53.3	$	3,425.4
Liabilities:
Derivative liabilities:
Foreign exchange contracts	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)
Total liabilities measured at fair value	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)

Total assets, reported as:
Cash equivalents	$	1,176.2	$	905.6		$	—	$	2,081.8		$	928.1	$	350.9		$	—	$	1,279.0
Short-term investments	229.4		657.9			—		887.3			247.5		778.6			—		1,026.1
Long-term investments	22.5		236.5			—		259.0			74.8		913.6			—		988.4
Prepaid expenses and other current assets	11.5		3.6			—		15.1			36.3		9.2			—		45.5
Other long-term assets	28.1		—			54.0		82.1			33.1		—			53.3		86.4
Total assets measured at fair value	$	1,467.7	$	1,803.6		$	54.0	$	3,325.3		$	1,319.8	$	2,052.3		$	53.3	$	3,425.4

Total liabilities, reported as:
Other accrued liabilities	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)
Total liabilities measured at fair value	$	—	$	(9.6	)	$	—	$	(9.6	)	$	—	$	(1.8	)	$	—	$	(1.8	)

________________________________


⁽¹⁾	Balance includes $11.6 million and $16.8 million in restricted investments measured at fair value, related to the Company's acquisition-related escrows as of September 30, 2018 and December 31, 2017, respectively. The December 31, 2017 balance also includes $25.0 million related to the Company's Directors and Officers indemnification trust, which was subsequently terminated.


⁽²⁾	Balance relates to restricted investments measured at fair value related to the Company's NQDC plan.

Derivative Instruments (Tables)

9 Months Ended

Sep. 30, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative instruments

The notional amount of the Company's foreign currency derivatives are summarized as follows (in millions):



	As of
	September 30, 2018		December 31, 2017
Cash flow hedges	$	609.5	$	521.1
Non-designated derivatives	141.4		108.3
Total	$	750.9	$	629.4

- Definition

Tabular disclosure of pertinent information about a derivative or group of derivatives on a disaggregated basis, such as for individual instruments, or small groups of similar instruments. May include a combination of the type of instrument, risks being hedged, notional amount, hedge designation, related hedged item, inception date, maturity date, or other relevant item.

+ References

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+ Details

Other Financial Information (Tables)

9 Months Ended

Sep. 30, 2018

Other Financial Information [Abstract]

Inventories

Total inventory consisted of the following (in millions):



	As of
	September 30, 2018		December 31, 2017
Production and service materials	$	56.3	$	71.2
Finished goods	19.3		26.6
Inventory	$	75.6	$	97.8

Reported as:
Prepaid expenses and other current assets	$	74.1	$	93.8
Other long-term assets	1.5		4.0
Total	$	75.6	$	97.8

Warranties

Changes during the nine months ended September 30, 2018 in the Company’s warranty reserve as reported within other accrued liabilities in the Condensed Consolidated Balance Sheets were as follows (in millions):



Balance as of December 31, 2017	$	27.4
Provisions made during the period	22.0
Actual costs incurred during the period	(23.0		)
Balance as of September 30, 2018	$	26.4

Deferred revenue

Details of the Company's deferred revenue, as reported in the Condensed Consolidated Balance Sheets, were as follows (in millions):



	As of
	September 30, 2018			December 31, 2017
Deferred product revenue:
Undelivered product commitments and other product deferrals	$	144.5		$	312.6
Distributor inventory and other sell-through items	—			68.1
Deferred gross product revenue	144.5			380.7
Deferred cost of product revenue	(10.9		)	(46.5		)
Deferred product revenue, net	133.6			334.2
Deferred service revenue	1,031.7			1,205.1
Total	$	1,165.3		$	1,539.3
Reported as:
Current	$	814.1		$	1,030.3
Long-term	351.2			509.0
Total	$	1,165.3		$	1,539.3

Performance obligation

The following table summarizes the transaction price for contracts that have not yet been recognized as revenue as of September 30, 2018 and when the Company expects to recognize the amounts as revenue (in millions):



	Revenue Recognition Expected by Period
	Total		Less than 1 year		1-3 years		More than 3 years
Product	$	144.5	$	119.5	$	22.1	$	2.9
Service	1,031.7		705.5		292.2		34.0
Total	$	1,176.2	$	825.0	$	314.3	$	36.9

Other expense, net

Other expense, net, consisted of the following (in millions):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Interest income	$	18.9		$	14.7		$	49.8		$	37.1
Interest expense	(25.8		)	(25.3		)	(77.7		)	(75.6		)
(Loss) gain on investments, net	(1.9		)	4.7			(1.8		)	6.7
Other	0.7			0.8			(1.4		)	(2.0		)
Other expense, net	$	(8.1	)	$	(5.1	)	$	(31.1	)	$	(33.8	)

Restructuring (Benefits) Charges (Tables)

9 Months Ended

Sep. 30, 2018

Restructuring and Related Activities [Abstract]

Schedule of restructuring liabilities

The following table provides a summary of changes in the restructuring liabilities for the Company's 2018 and 2017 restructuring plans (in millions):



	December 31, 2017		Charges/ (Benefits)			Cash Payments			Other		September 30, 2018
Severance	$	17.7	$	3.3		$	(19.3	)	$	0.1	$	1.8
Contract terminations and other	2.3		(1.0		)	(1.3		)	—		—
Total	$	20.0	$	2.3		$	(20.6	)	$	0.1	$	1.8

Equity (Tables)

9 Months Ended

Sep. 30, 2018

Stockholders' Equity Note [Abstract]

Cash Dividends Declared

The following table summarizes the Company’s cash dividends declared per common stock:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cash dividends declared per common stock	$	0.18	$	0.10	$	0.54	$	0.30

Schedule of repurchase agreements

The following table summarizes the Company's stock repurchases and retirements under its stock repurchase programs (in millions, except per share amounts):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018 ⁽¹⁾		2017 ⁽²⁾		2018 ⁽¹⁾		2017 ⁽²⁾
Shares repurchased	6.0		5.0		29.3		13.5
Average price per share	$	25.62	$	28.16	$	25.62	$	28.85
Amount repurchased	$	—	$	140.0	$	750.0	$	390.0

________________________________

⁽¹⁾Shares repurchased under the 2018 Stock Repurchase Program. $750.0 million represents the full amount of the ASR for which 23.3 million shares were received initially during the first quarter of 2018, and an additional 6.0 million shares were received at final settlement during the third quarter of 2018.

⁽²⁾Shares repurchased under the 2014 Stock Repurchase Program.

Components of accumulated other comprehensive loss, net of taxes

The components of accumulated other comprehensive loss, net of related taxes, for the nine months ended September 30, 2018 were as follows (in millions):



	Unrealized Gains/Losses on Available-for- Sale Debt Securities⁽¹⁾			Unrealized Gains/Losses on Cash Flow Hedges⁽²⁾			Foreign Currency Translation Adjustments			Total
Balance as of December 31, 2017	$	19.0		$	6.0		$	(30.4	)	$	(5.4	)
Other comprehensive loss before reclassifications	(0.6		)	(5.9		)	(13.7		)	(20.2		)
Amount reclassified from accumulated other comprehensive loss	0.9			(5.5		)	—			(4.6		)
Other comprehensive income (loss), net	0.3			(11.4		)	(13.7		)	(24.8		)
Reclassification of tax effects upon adoption of ASU 2018-02	5.0			0.7			—			5.7
Balance as of September 30, 2018	$	24.3		$	(4.7	)	$	(44.1	)	$	(24.5	)

________________________________


⁽¹⁾	The reclassifications out of accumulated other comprehensive loss during the nine months ended September 30, 2018 for realized gains/losses on available-for-sale debt securities were included in other expense, net, in the Condensed Consolidated Statements of Operations and were not material.


⁽²⁾	The reclassifications out of accumulated other comprehensive loss during the nine months ended September 30, 2018 for realized gains/losses on cash flow hedges were included within cost of revenues, research and development, sales and marketing, and general and administrative in the Condensed Consolidated Statements of Operations and were not material individually.

Employee Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2018

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

Schedule of share-based compensation, stock options, activity

The following table summarizes the Company’s stock option activity and related information as of and for the nine months ended September 30, 2018 (in millions, except for per share amounts and years):



	Outstanding Options
	Number of Shares		Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (In Years)	Aggregate Intrinsic Value
Balance as of December 31, 2017	0.9		$	34.41
Exercised	(0.1	)	4.20
Expired/Canceled	(0.7	)	40.34
Balance as of September 30, 2018	0.1		$	19.80	1.9	$	1.2

As of September 30, 2018:
Vested and expected-to-vest options	0.1		$	19.80	1.9	$	1.2
Exercisable options	0.1		$	22.24	1.0	$	0.8

Schedule of nonvested share activity

The Company’s RSU and PSA activity and related information as of and for the nine months ended September 30, 2018 were as follows (in millions, except per share amounts and years):



	Outstanding RSUs and PSAs⁽⁴⁾
	Number of Shares		Weighted Average Grant-Date Fair Value per Share		Weighted Average Remaining Contractual Term (In Years)	Aggregate Intrinsic Value
Balance as of December 31, 2017	19.5		$	25.39
RSUs granted ⁽¹⁾⁽³⁾	6.5		25.36
PSAs granted⁽²⁾⁽³⁾	0.7		24.43
RSUs vested	(5.4	)	25.43
PSAs vested	(1.1	)	24.14
RSUs canceled	(1.5	)	26.34
PSAs canceled	(0.7	)	24.39
Balance as of September 30, 2018	18.0		$	25.37	1.1	$	538.8

________________________________

⁽¹⁾

Includes service-based and market-based RSUs. The number of shares subject to market-based condition represents the aggregate maximum number of shares that may be issued pursuant to the award over its full term. The aggregate number of shares subject to market-based condition that would be issued if market criteria determined by the Compensation Committee of the Board are achieved at target is 0.1 million shares. Depending on achievement of such performance goals, the range of shares that could be issued under these awards is zero to 0.3 million shares.

⁽²⁾

The number of shares subject to PSAs granted represents the aggregate maximum number of shares that may be issued pursuant to the award over its full term. The aggregate number of shares subject to these PSAs that would be issued if performance goals determined by the Compensation Committee of the Board are achieved at target is 0.4 million shares. Depending on achievement of such performance goals, the range of shares that could be issued under these awards is zero to 0.7 million shares.

⁽³⁾

The grant date fair value of RSUs and PSAs were reduced by the present value of dividends expected to be paid on the underlying shares of common stock during the requisite and derived service period as these awards are not entitled to receive dividends until vested. During the nine months ended September 30, 2018, the Company declared a quarterly cash dividend of $0.18 per share of common stock on January 30, 2018, May 2, 2018, and July 26, 2018.

⁽⁴⁾

2.0 million shares of PSAs were modified during the nine months ended September 30, 2018, which relate primarily to PSAs assumed by the Company in connection with acquisitions consummated in 2016. These awards are contingent upon the achievement of certain performance milestones. Compensation cost resulting from the modifications totaled $6.3 million to be recognized over the remaining terms of the modified awards.

Summary of employee stock purchases through the ESPP

The following table summarizes employee stock purchases through the ESPP (in millions, except per share amounts):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Shares purchased	1.2		1.2		2.5		2.7
Average exercise price per share	$	22.39	$	22.79	$	22.31	$	20.83

Schedule of employee service share-based compensation, allocation of recognized period costs

Share-based compensation expense associated with stock options, RSUs, restricted stock awards ("RSAs"), PSAs, and the ESPP was recorded in the following cost and expense categories in the Condensed Consolidated Statements of Operations (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenues - Product	$	1.5	$	1.5	$	5.1	$	3.8
Cost of revenues - Service	4.5		3.9		14.2		13.5
Research and development	28.1		18.5		101.8		67.4
Sales and marketing	12.9		13.7		40.4		45.3
General and administrative	6.2		7.4		18.7		21.1
Total	$	53.2	$	45.0	$	180.2	$	151.1

Disclosure of share-based compensation arrangements by share-based payment award

The following table summarizes share-based compensation expense by award type (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Stock options	$	0.1	$	0.2	$	0.3	$	0.5
RSUs, RSAs, and PSAs	48.2		41.0		165.8		138.9
ESPP	4.9		3.8		14.1		11.7
Total	$	53.2	$	45.0	$	180.2	$	151.1

Segments (Tables)

9 Months Ended

Sep. 30, 2018

Segment Reporting [Abstract]

Financial information for each segment

The following table presents net revenues by product and service (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Routing	$	496.4	$	585.8	$	1,395.1	$	1,679.9
Switching	221.1		212.6		705.9		730.2
Security	77.2		71.3		229.4		205.7
Total product	794.7		869.7		2,330.4		2,615.8

Total service	385.1		388.1		1,136.1		1,171.9
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

The following table presents net revenues by customer vertical (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cloud	$	250.0	$	344.9	$	798.1	$	1,056.1
Service Provider	543.6		576.9		1,546.8		1,707.8
Enterprise	386.2		336.0		1,121.6		1,023.8
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

Disaggregation of revenue

The following table presents net revenues by product and service (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Routing	$	496.4	$	585.8	$	1,395.1	$	1,679.9
Switching	221.1		212.6		705.9		730.2
Security	77.2		71.3		229.4		205.7
Total product	794.7		869.7		2,330.4		2,615.8

Total service	385.1		388.1		1,136.1		1,171.9
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

The following table presents net revenues by customer vertical (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cloud	$	250.0	$	344.9	$	798.1	$	1,056.1
Service Provider	543.6		576.9		1,546.8		1,707.8
Enterprise	386.2		336.0		1,121.6		1,023.8
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

The Company attributes revenues to geographic region based on the customer’s shipping address. The following table presents net revenues by geographic region (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Americas:
United States	$	597.1	$	668.8	$	1,754.2	$	2,076.0
Other	46.0		60.4		152.2		165.6
Total Americas	643.1		729.2		1,906.4		2,241.6
Europe, Middle East, and Africa	329.9		298.6		946.8		871.3
Asia Pacific	206.8		230.0		613.3		674.8
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

Net revenues by geographic region

The Company attributes revenues to geographic region based on the customer’s shipping address. The following table presents net revenues by geographic region (in millions):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Americas:
United States	$	597.1	$	668.8	$	1,754.2	$	2,076.0
Other	46.0		60.4		152.2		165.6
Total Americas	643.1		729.2		1,906.4		2,241.6
Europe, Middle East, and Africa	329.9		298.6		946.8		871.3
Asia Pacific	206.8		230.0		613.3		674.8
Total	$	1,179.8	$	1,257.8	$	3,466.5	$	3,787.7

Income Taxes (Tables)

9 Months Ended

Sep. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of effective income tax rate reconciliation

The following table provides details of income taxes (in millions, except percentages):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Income before income taxes	$	152.0		$	225.8		$	344.3		$	611.6
Income tax (benefit) provision	$	(71.8	)	$	60.1		$	(30.4	)	$	157.3
Effective tax (benefit) rate	(47.2		)%	26.6		%	(8.8		)%	25.7		%

Net Income Per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Schedule of basic and diluted net income per share

The Company computed basic and diluted net income per share as follows (in millions, except per share amounts):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Numerator:
Net income	$	223.8	$	165.7	$	374.7	$	454.3
Denominator:
Weighted-average shares used to compute basic net income per share	346.2		378.3		350.1		380.0
Dilutive effect of employee stock awards	4.3		4.4		5.1		6.5
Weighted-average shares used to compute diluted net income per share	350.5		382.7		355.2		386.5
Net income per share
Basic	$	0.65	$	0.44	$	1.07	$	1.20
Diluted	$	0.64	$	0.43	$	1.05	$	1.18

Anti-dilutive shares	4.2		1.0		5.0		1.2

Basis of Presentation (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Restricted cash	$ 54.2	$ 47.4

Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018
Accumulated Deficit \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	$ 324.7
Cumulative effect on retained earnings, tax	63.9
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, terms of payment (in days)		30 days
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, terms of payment (in days)		90 days
Accumulated Other Comprehensive Loss
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of taxes effects upon adoption of ASU 2018-02, net		$ 5.7
Accumulated Other Comprehensive Loss \| Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of taxes effects upon adoption of ASU 2018-02, net	5.7
Accumulated Deficit \| Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of taxes effects upon adoption of ASU 2018-02, net	$ (5.7)

Summary of Significant Accounting Policies - Contract Revenue Adjustments on Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Accounts receivable, net of allowances	$ 648.3	$ 850.1	$ 852.0
Prepaid expenses and other current assets	253.4	331.4	299.9
Other long-term assets	373.7	394.4	415.5
Total assets	9,100.3	9,842.3	9,833.8
Liabilities:
Deferred revenue	814.1	804.9	1,030.3
Other accrued liabilities	214.8	338.1	304.3
Long-term deferred revenue	351.2	384.4	509.0
Total liabilities	4,449.4	4,836.7	5,152.9
Stockholders' Equity:
Accumulated deficit	(3,023.0)	(3,031.1)	(3,355.8)
As reported/Without Adoption of Topic 606
Assets:
Accounts receivable, net of allowances	635.3		852.0
Prepaid expenses and other current assets	232.6		299.9
Other long-term assets	371.8		415.5
Total assets	9,064.6		9,833.8
Liabilities:
Deferred revenue	1,044.7		1,030.3
Other accrued liabilities	161.2		304.3
Long-term deferred revenue	445.5		509.0
Total liabilities	4,720.7		5,152.9
Stockholders' Equity:
Accumulated deficit	(3,330.2)		$ (3,355.8)
Adjustments/ Topic 606 Impact \| Accounting Standards Update 2014-09
Assets:
Accounts receivable, net of allowances	13.0	(1.9)
Prepaid expenses and other current assets	20.8	31.5
Other long-term assets	1.9	(21.1)
Total assets	35.7	8.5
Liabilities:
Deferred revenue	(230.6)	(225.4)
Other accrued liabilities	53.6	33.8
Long-term deferred revenue	(94.3)	(124.6)
Total liabilities	(271.3)	(316.2)
Stockholders' Equity:
Accumulated deficit	$ 307.2	$ 324.7

Summary of Significant Accounting Policies - Contract Revenue Adjustments on Income Statement (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net revenues:
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Operating expenses:
Sales and marketing	224.8	232.5	702.5	716.6
Without Adoption of Topic 606
Net revenues:
Total net revenues	1,184.4		3,486.0
Operating expenses:
Sales and marketing	225.4		697.6
Topic 606 Impact \| Accounting Standards Update 2014-09
Net revenues:
Total net revenues	(4.6)		(19.5)
Operating expenses:
Sales and marketing	(0.6)		4.9
Product
Net revenues:
Total net revenues	794.7	869.7	2,330.4	2,615.8
Product \| Without Adoption of Topic 606
Net revenues:
Total net revenues	771.9		2,249.7
Product \| Topic 606 Impact \| Accounting Standards Update 2014-09
Net revenues:
Total net revenues	22.8		80.7
Service
Net revenues:
Total net revenues	385.1	$ 388.1	1,136.1	$ 1,171.9
Service \| Without Adoption of Topic 606
Net revenues:
Total net revenues	412.5		1,236.3
Service \| Topic 606 Impact \| Accounting Standards Update 2014-09
Net revenues:
Total net revenues	$ (27.4)		$ (100.2)

Cash Equivalents and Investments - Available-For-Sale (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Available-for-sale debt securities:
Amortized Cost	$ 2,135.5	$ 2,386.3
Gross Unrealized Gains	37.4	37.9
Gross Unrealized Losses	(5.4)	(5.4)
Estimated Fair Value	2,167.5	2,418.8
Asset-backed securities
Available-for-sale debt securities:
Amortized Cost	71.9	287.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.4)	(0.6)
Estimated Fair Value	71.5	286.5
Certificates of deposit
Available-for-sale debt securities:
Amortized Cost	96.7	83.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	96.7	83.8
Commercial paper
Available-for-sale debt securities:
Amortized Cost	334.7	217.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	334.7	217.1
Corporate debt securities
Available-for-sale debt securities:
Amortized Cost	450.4	929.6
Gross Unrealized Gains	0.0	0.4
Gross Unrealized Losses	(3.7)	(3.0)
Estimated Fair Value	446.7	927.0
Foreign government debt securities
Available-for-sale debt securities:
Amortized Cost	23.0	62.9
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.2)	(0.2)
Estimated Fair Value	22.8	62.7
Time deposits
Available-for-sale debt securities:
Amortized Cost	309.3	239.2
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	309.3	239.2
U.S. government agency securities
Available-for-sale debt securities:
Amortized Cost	101.8	143.9
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.3)	(0.7)
Estimated Fair Value	101.5	143.2
U.S. government securities
Available-for-sale debt securities:
Amortized Cost	731.1	406.8
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	(0.8)	(0.9)
Estimated Fair Value	730.3	406.0
Fixed Income securities
Available-for-sale debt securities:
Amortized Cost	2,118.9	2,370.4
Gross Unrealized Gains	0.0	0.5
Gross Unrealized Losses	(5.4)	(5.4)
Estimated Fair Value	2,113.5	2,365.5
Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Amortized Cost	16.6	15.9
Gross Unrealized Gains	37.4	37.4
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	54.0	53.3
Cash equivalents
Available-for-sale debt securities:
Amortized Cost	967.2	351.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	967.2	351.0
Short-term investments
Available-for-sale debt securities:
Amortized Cost	889.5	1,027.2
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	(2.2)	(1.2)
Estimated Fair Value	887.3	1,026.1
Long-term investments
Available-for-sale debt securities:
Amortized Cost	262.2	992.2
Gross Unrealized Gains	0.0	0.4
Gross Unrealized Losses	(3.2)	(4.2)
Estimated Fair Value	259.0	988.4
Other long-term assets
Available-for-sale debt securities:
Amortized Cost	16.6	15.9
Gross Unrealized Gains	37.4	37.4
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	$ 54.0	$ 53.3

Cash Equivalents and Investments - Maturities of Fixed Income Securities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Amortized Cost	$ 2,135.5	$ 2,386.3
Estimated Fair Value
Total	2,167.5	2,418.8
Fixed Income Securities
Amortized Cost
Due in less than one year	1,856.7
Due between one and five years	262.2
Amortized Cost	2,118.9	2,370.4
Estimated Fair Value
Due in less than one year	1,854.5
Due between one and five years	259.0
Total	$ 2,113.5	$ 2,365.5

Cash Equivalents and Investments - Unrealized Loss Position on Fixed Income Securities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fixed Income Securities
Fair Value
Less than 12 Months	$ 989.4	$ 1,238.3
12 Months or Greater	292.8	273.3
Total	1,282.2	1,511.6
Unrealized Loss
Less than 12 Months	(2.8)	(3.6)
12 Months or Greater	(2.6)	(1.8)
Total	(5.4)	(5.4)
Asset-backed securities
Fair Value
Less than 12 Months	16.9	215.2
12 Months or Greater	46.5	38.4
Total	63.4	253.6
Unrealized Loss
Less than 12 Months	(0.1)	(0.4)
12 Months or Greater	(0.3)	(0.2)
Total	(0.4)	(0.6)
Commercial paper
Fair Value
Less than 12 Months	0.8
12 Months or Greater	0.0
Total	0.8
Unrealized Loss
Less than 12 Months	0.0
12 Months or Greater	0.0
Total	0.0
Corporate debt securities
Fair Value
Less than 12 Months	279.0	646.7
12 Months or Greater	136.9	108.6
Total	415.9	755.3
Unrealized Loss
Less than 12 Months	(2.3)	(2.1)
12 Months or Greater	(1.4)	(0.9)
Total	(3.7)	(3.0)
Foreign government debt securities
Fair Value
Less than 12 Months	8.0	47.3
12 Months or Greater	13.4	6.6
Total	21.4	53.9
Unrealized Loss
Less than 12 Months	0.0	(0.2)
12 Months or Greater	(0.2)	0.0
Total	(0.2)	(0.2)
U.S. government agency securities
Fair Value
Less than 12 Months	67.8	68.3
12 Months or Greater	33.6	67.9
Total	101.4	136.2
Unrealized Loss
Less than 12 Months	(0.1)	(0.2)
12 Months or Greater	(0.2)	(0.5)
Total	(0.3)	(0.7)
U.S. government securities
Fair Value
Less than 12 Months	616.9	260.8
12 Months or Greater	62.4	51.8
Total	679.3	312.6
Unrealized Loss
Less than 12 Months	(0.3)	(0.7)
12 Months or Greater	(0.5)	(0.2)
Total	$ (0.8)	$ (0.9)

Cash Equivalents and Investments - Narrative (Details)	3 Months Ended		9 Months Ended
Cash Equivalents and Investments - Narrative (Details)	Sep. 30, 2018 USD ($) Investment	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Investment	Sep. 30, 2017 USD ($)
Restricted Cash and Cash Equivalents Items [Line Items]
Total investments in unrealized loss position \| Investment	539		539
Available-for-sale debt securities, gross realized gain	$ 0	$ 0	$ 0	$ 0
Available-for-sale debt securities, gross realized loss	0	0	0	0
Equity investments, unrealized gains	0	0	0	0
Equity investments, unrealized losses	0	0	0	0
Restricted cash and investments	60,700,000		60,700,000
Prepaid expenses and other current assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	26,600,000		26,600,000
Other long-term assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and investments	34,100,000		34,100,000
Debt Securities
Restricted Cash and Cash Equivalents Items [Line Items]
OTTI, associated with credit losses	$ 0	$ 0	$ 0	$ 0

Cash Equivalents and Investments - Equity securities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments without readily determinable fair value	$ 32.6
Total equity securities	1,186.8
Equity investments without readily determinable fair value		$ 29.7
Total equity securities		1,027.1
Money market funds
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments with readily determinable fair value	1,126.2
Equity investments with readily determinable fair value		969.8
Mutual funds
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments with readily determinable fair value	28.0
Equity investments with readily determinable fair value		27.6
Cash equivalents
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	1,114.6
Total equity securities		928.0
Prepaid expenses and other current assets
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	11.5
Total equity securities		36.3
Other long-term assets
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	$ 60.7
Total equity securities		$ 62.8

Cash Equivalents and Investments - Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 2,501.7	$ 2,006.5
Restricted cash			$ 54.2	$ 47.4
Total cash, cash equivalents, and restricted cash	2,522.8	2,059.1	$ 2,417.9	$ 1,880.6
Prepaid expenses and other current assets
Cash and Cash Equivalents [Line Items]
Restricted cash	15.1	49.6
Other long-term assets
Cash and Cash Equivalents [Line Items]
Restricted cash	$ 6.0	$ 3.0

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Available-for-sale securities:
Available-for-sale debt securities	$ 2,167.5	$ 2,418.8
Asset-backed securities
Available-for-sale securities:
Available-for-sale debt securities	71.5	286.5
Certificates of deposit
Available-for-sale securities:
Available-for-sale debt securities	96.7	83.8
Commercial paper
Available-for-sale securities:
Available-for-sale debt securities	334.7	217.1
Corporate debt securities
Available-for-sale securities:
Available-for-sale debt securities	446.7	927.0
Foreign government debt securities
Available-for-sale securities:
Available-for-sale debt securities	22.8	62.7
Time deposits
Available-for-sale securities:
Available-for-sale debt securities	309.3	239.2
U.S. government agency securities
Available-for-sale securities:
Available-for-sale debt securities	101.5	143.2
U.S. government securities
Available-for-sale securities:
Available-for-sale debt securities	730.3	406.0
Privately-held debt and redeemable preferred stock securities
Available-for-sale securities:
Available-for-sale debt securities	54.0	53.3
Money market funds
Available-for-sale securities:
Equity securities	1,126.2
Equity securities		969.8
Fair Value, Measurements, Recurring
Available-for-sale securities:
Equity securities	1,154.2
Equity securities		997.4
Derivative assets:
Total assets measured at fair value	3,325.3	3,425.4
Liabilities measured at fair value:
Total liabilities measured at fair value	(9.6)	(1.8)
Fair Value, Measurements, Recurring \| Foreign exchange contracts
Derivative assets:
Foreign exchange contracts	3.6	9.2
Liabilities measured at fair value:
Derivative liabilities	(9.6)	(1.8)
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Equity securities	1,154.2
Equity securities		997.4
Derivative assets:
Total assets measured at fair value	1,467.7	1,319.8
Liabilities measured at fair value:
Total liabilities measured at fair value	0.0	0.0
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1) \| Foreign exchange contracts
Derivative assets:
Foreign exchange contracts	0.0	0.0
Liabilities measured at fair value:
Derivative liabilities	0.0	0.0
Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Equity securities	0.0
Equity securities		0.0
Derivative assets:
Total assets measured at fair value	1,803.6	2,052.3
Liabilities measured at fair value:
Total liabilities measured at fair value	(9.6)	(1.8)
Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2) \| Foreign exchange contracts
Derivative assets:
Foreign exchange contracts	3.6	9.2
Liabilities measured at fair value:
Derivative liabilities	(9.6)	(1.8)
Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Equity securities	0.0
Equity securities		0.0
Derivative assets:
Total assets measured at fair value	54.0	53.3
Liabilities measured at fair value:
Total liabilities measured at fair value	0.0	0.0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3) \| Foreign exchange contracts
Derivative assets:
Foreign exchange contracts	0.0	0.0
Liabilities measured at fair value:
Derivative liabilities	0.0	0.0
Fair Value, Measurements, Recurring \| Asset-backed securities
Available-for-sale securities:
Available-for-sale debt securities	71.5	286.5
Fair Value, Measurements, Recurring \| Asset-backed securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Asset-backed securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	71.5	286.5
Fair Value, Measurements, Recurring \| Asset-backed securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Certificates of deposit
Available-for-sale securities:
Available-for-sale debt securities	96.7	83.8
Fair Value, Measurements, Recurring \| Certificates of deposit \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Certificates of deposit \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	96.7	83.8
Fair Value, Measurements, Recurring \| Certificates of deposit \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Commercial paper
Available-for-sale securities:
Available-for-sale debt securities	334.7	217.1
Fair Value, Measurements, Recurring \| Commercial paper \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Commercial paper \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	334.7	217.1
Fair Value, Measurements, Recurring \| Commercial paper \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Corporate debt securities
Available-for-sale securities:
Available-for-sale debt securities	446.7	927.0
Fair Value, Measurements, Recurring \| Corporate debt securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Corporate debt securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	446.7	927.0
Fair Value, Measurements, Recurring \| Corporate debt securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Foreign government debt securities
Available-for-sale securities:
Available-for-sale debt securities	22.8	62.7
Fair Value, Measurements, Recurring \| Foreign government debt securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Foreign government debt securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	22.8	62.7
Fair Value, Measurements, Recurring \| Foreign government debt securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Time deposits
Available-for-sale securities:
Available-for-sale debt securities	309.3	239.2
Fair Value, Measurements, Recurring \| Time deposits \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Time deposits \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	309.3	239.2
Fair Value, Measurements, Recurring \| Time deposits \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| U.S. government agency securities
Available-for-sale securities:
Available-for-sale debt securities	101.5	143.2
Fair Value, Measurements, Recurring \| U.S. government agency securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| U.S. government agency securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	101.5	143.2
Fair Value, Measurements, Recurring \| U.S. government agency securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| U.S. government securities
Available-for-sale securities:
Available-for-sale debt securities	730.3	406.0
Fair Value, Measurements, Recurring \| U.S. government securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	313.5	322.4
Fair Value, Measurements, Recurring \| U.S. government securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	416.8	83.6
Fair Value, Measurements, Recurring \| U.S. government securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Privately-held debt and redeemable preferred stock securities
Available-for-sale securities:
Available-for-sale debt securities	54.0	53.3
Fair Value, Measurements, Recurring \| Privately-held debt and redeemable preferred stock securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Privately-held debt and redeemable preferred stock securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring \| Privately-held debt and redeemable preferred stock securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	54.0	53.3
Fair Value, Measurements, Recurring \| Total available-for-sale debt securities
Available-for-sale securities:
Available-for-sale debt securities	2,167.5	2,418.8
Fair Value, Measurements, Recurring \| Total available-for-sale debt securities \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Available-for-sale debt securities	313.5	322.4
Fair Value, Measurements, Recurring \| Total available-for-sale debt securities \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Available-for-sale debt securities	1,800.0	2,043.1
Fair Value, Measurements, Recurring \| Total available-for-sale debt securities \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Available-for-sale debt securities	54.0	53.3
Fair Value, Measurements, Recurring \| Money market funds
Available-for-sale securities:
Equity securities	1,126.2
Equity securities		969.8
Fair Value, Measurements, Recurring \| Money market funds \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Equity securities	1,126.2
Equity securities		969.8
Fair Value, Measurements, Recurring \| Money market funds \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Equity securities	0.0
Equity securities		0.0
Fair Value, Measurements, Recurring \| Money market funds \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Equity securities	0.0
Equity securities		0.0
Fair Value, Measurements, Recurring \| Mutual funds
Available-for-sale securities:
Equity securities	28.0
Equity securities		27.6
Fair Value, Measurements, Recurring \| Mutual funds \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale securities:
Equity securities	28.0
Equity securities		27.6
Fair Value, Measurements, Recurring \| Mutual funds \| Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale securities:
Equity securities	0.0
Equity securities		0.0
Fair Value, Measurements, Recurring \| Mutual funds \| Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale securities:
Equity securities	0.0
Equity securities		0.0
Cash equivalents
Available-for-sale securities:
Available-for-sale debt securities	967.2	351.0
Cash equivalents \| Fair Value, Measurements, Recurring
Derivative assets:
Total assets measured at fair value	2,081.8	1,279.0
Cash equivalents \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Derivative assets:
Total assets measured at fair value	1,176.2	928.1
Cash equivalents \| Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Derivative assets:
Total assets measured at fair value	905.6	350.9
Cash equivalents \| Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Derivative assets:
Total assets measured at fair value	0.0	0.0
Short-term investments
Available-for-sale securities:
Available-for-sale debt securities	887.3	1,026.1
Short-term investments \| Fair Value, Measurements, Recurring
Derivative assets:
Total assets measured at fair value	887.3	1,026.1
Short-term investments \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Derivative assets:
Total assets measured at fair value	229.4	247.5
Short-term investments \| Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Derivative assets:
Total assets measured at fair value	657.9	778.6
Short-term investments \| Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Derivative assets:
Total assets measured at fair value	0.0	0.0
Long-term investments
Available-for-sale securities:
Available-for-sale debt securities	259.0	988.4
Long-term investments \| Fair Value, Measurements, Recurring
Derivative assets:
Total assets measured at fair value	259.0	988.4
Long-term investments \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Derivative assets:
Total assets measured at fair value	22.5	74.8
Long-term investments \| Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Derivative assets:
Total assets measured at fair value	236.5	913.6
Long-term investments \| Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Derivative assets:
Total assets measured at fair value	0.0	0.0
Prepaid expenses and other current assets \| Fair Value, Measurements, Recurring
Derivative assets:
Total assets measured at fair value	15.1	45.5
Prepaid expenses and other current assets \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Derivative assets:
Total assets measured at fair value	11.5	36.3
Prepaid expenses and other current assets \| Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Derivative assets:
Total assets measured at fair value	3.6	9.2
Prepaid expenses and other current assets \| Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Derivative assets:
Total assets measured at fair value	0.0	0.0
Other long-term assets \| Fair Value, Measurements, Recurring
Derivative assets:
Total assets measured at fair value	82.1	86.4
Other long-term assets \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Derivative assets:
Total assets measured at fair value	28.1	33.1
Other long-term assets \| Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Derivative assets:
Total assets measured at fair value	0.0	0.0
Other long-term assets \| Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Derivative assets:
Total assets measured at fair value	54.0	53.3
Other accrued liabilities \| Fair Value, Measurements, Recurring
Liabilities measured at fair value:
Total liabilities measured at fair value	(9.6)	(1.8)
Other accrued liabilities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets For Identical Assets (Level 1)
Liabilities measured at fair value:
Total liabilities measured at fair value	0.0	0.0
Other accrued liabilities \| Fair Value, Measurements, Recurring \| Significant Other Observable Remaining Inputs (Level 2)
Liabilities measured at fair value:
Total liabilities measured at fair value	(9.6)	(1.8)
Other accrued liabilities \| Fair Value, Measurements, Recurring \| Significant Other Unobservable Remaining Inputs (Level 3)
Liabilities measured at fair value:
Total liabilities measured at fair value	$ 0.0	$ 0.0

Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
Fair Value Measurements - Narrative (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Acquisition-related escrows	$ 11,600,000	$ 11,600,000		$ 16,800,000
Indemnification trust				25,000,000
Goodwill and intangible impairment	0	0
Equity securities without readily determinable fair value, impairment	0	0	$ 0
Equity securities without readily determinable fair value, upward adjustment	0	0
Equity securities without readily determinable fair value, downward adjustment	0	0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial and nonfinancial liabilities, fair value disclosure	9,600,000	9,600,000		1,800,000
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial and nonfinancial liabilities, fair value disclosure	0	0		0
Significant Other Unobservable Remaining Inputs (Level 3) \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial and nonfinancial liabilities, fair value disclosure	0	0		0
Significant Other Observable Remaining Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term and long-term debt, fair value	2,168,400,000	2,168,400,000		2,252,900,000
Significant Other Observable Remaining Inputs (Level 2) \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial and nonfinancial liabilities, fair value disclosure	9,600,000	9,600,000		1,800,000
Privately-held debt and redeemable preferred stock securities \| Significant Other Unobservable Remaining Inputs (Level 3) \| Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on investments	0	0
Junos Pulse
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note receivable	$ 64,600,000	$ 64,600,000		$ 61,200,000

Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivatives, Notional Amount [Line Items]
Notional amount of foreign currency derivatives	$ 750.9		$ 750.9		$ 629.4
Non-designated derivatives
Derivatives, Notional Amount [Line Items]
Notional amount of foreign currency derivatives	141.4		141.4		108.3
Cash flow hedges \| Designated as hedge
Derivatives, Notional Amount [Line Items]
Notional amount of foreign currency derivatives	609.5		$ 609.5		$ 521.1
Maturities of cash flow hedge derivatives			18 months
Losses expected to be reclassified into earnings within the next 12 months			$ 5.8
Foreign exchange contracts \| Cash flow hedges
Derivatives, Notional Amount [Line Items]
Derivative instruments, gain (loss) recognized in other comprehensive income (loss), Effective portion	(6.1)	$ 6.8	(8.6)	$ 17.6
Cost of revenues and operating expenses \| Foreign exchange contracts \| Cash flow hedges
Derivatives, Notional Amount [Line Items]
Gain (loss) reclassified	$ (3.1)	$ 0.0	$ 5.8	$ 0.0

Other Financial Information - Inventories, Net (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Inventory [Line Items]
Production and service materials	$ 56.3	$ 71.2
Finished goods	19.3	26.6
Inventory	75.6	97.8
Prepaid expenses and other current assets
Schedule Of Inventory [Line Items]
Inventory	74.1	93.8
Other long-term assets
Schedule Of Inventory [Line Items]
Inventory	$ 1.5	$ 4.0

Other Financial Information - Warranties (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance as of December 31, 2017	$ 27.4
Provisions made during the period	22.0
Actual costs incurred during the period	(23.0)
Balance as of September 30, 2018	$ 26.4

Other Financial Information - Deferred Revenue (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Reported as:
Current	$ 814.1	$ 804.9	$ 1,030.3
Long-term	351.2	$ 384.4	509.0
Deferred revenue	1,165.3		1,539.3
Undelivered product commitments and other product deferrals
Deferred product revenue:
Deferred gross product revenue	144.5		312.6
Distributor inventory and other sell-through items
Deferred product revenue:
Deferred gross product revenue	0.0		68.1
Product
Deferred product revenue:
Deferred gross product revenue	144.5		380.7
Deferred cost of product revenue	(10.9)		(46.5)
Reported as:
Deferred revenue	133.6		334.2
Service
Reported as:
Deferred revenue	$ 1,031.7		$ 1,205.1

Other Financial Information - Narrative (Details)	3 Months Ended	9 Months Ended
Other Financial Information - Narrative (Details)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Deferred commission	$ 26,900,000	$ 26,900,000
Amortization of deferred commission	31,200,000	109,400,000
Impairment loss	0	0
Product
Disaggregation of Revenue [Line Items]
Contract with customer, liability, revenue recognized	21,100,000	77,600,000
Service
Disaggregation of Revenue [Line Items]
Contract with customer, liability, revenue recognized	$ 150,000,000	$ 581,300,000

Other Financial Information - Revenue (Details) $ in Millions	Sep. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 825.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01 \| Product
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 119.5
Revenue recognition expected by period, satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01 \| Service
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 705.5
Revenue recognition expected by period, satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 314.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 \| Product
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 22.1
Revenue recognition expected by period, satisfaction period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 \| Service
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 292.2
Revenue recognition expected by period, satisfaction period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 36.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01 \| Product
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 2.9
Revenue recognition expected by period, satisfaction period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01 \| Service
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 34.0
Revenue recognition expected by period, satisfaction period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 1,176.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) \| Product
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	144.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) \| Service
Disaggregation of Revenue [Line Items]
Revenue recognition expected by period	$ 1,031.7

Other Financial Information - Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Financial Information [Abstract]
Interest income	$ 18.9	$ 14.7	$ 49.8	$ 37.1
Interest expense	(25.8)	(25.3)	(77.7)	(75.6)
(Loss) gain on investments, net	(1.9)	4.7	(1.8)	6.7
Other	0.7	0.8	(1.4)	(2.0)
Other expense, net	$ (8.1)	$ (5.1)	$ (31.1)	$ (33.8)

Restructuring Charges - Narrative (Details) - 2018 Restructuring Plan - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Severance costs		$ 4.9	$ 4.9
Forecast
Restructuring Cost and Reserve [Line Items]
Severance costs	$ 5.0

Restructuring Charges - Changes to Restructuring Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Reserve [Roll Forward]
Charges/ (Benefits)	$ 4.4	$ 2.0	$ 2.3	$ 29.4
2017 Restructuring Plan
Restructuring Reserve [Roll Forward]
Restructuring liability, beginning balance			20.0
Charges/ (Benefits)			2.3
Cash Payments			(20.6)
Other			0.1
Restructuring liability, ending balance	1.8		1.8
2017 Restructuring Plan \| Severance
Restructuring Reserve [Roll Forward]
Restructuring liability, beginning balance			17.7
Charges/ (Benefits)			3.3
Cash Payments			(19.3)
Other			0.1
Restructuring liability, ending balance	1.8		1.8
2017 Restructuring Plan \| Contract terminations and other
Restructuring Reserve [Roll Forward]
Restructuring liability, beginning balance			2.3
Charges/ (Benefits)			(1.0)
Cash Payments			(1.3)
Other			0.0
Restructuring liability, ending balance	$ 0.0		$ 0.0

Equity - Cash Dividends on Shares of Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended						9 Months Ended
	Jul. 26, 2018	May 02, 2018	Jan. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Stockholders' Equity Note [Abstract]
Cash dividends declared per common stock (in dollars per share)	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.1	$ 0.10	$ 0.10	$ 0.54	$ 0.3
Cash dividends paid per common stock (in dollars per share)				$ 0.18	$ 0.18	$ 0.18	$ 0.10	$ 0.10	$ 0.10
Common stock, dividends paid										$ 187.0	$ 113.5

Equity - Stock Repurchase Activities (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Feb. 28, 2018	Jan. 31, 2018
Accelerated Share Repurchases [Line Items]
Payment to repurchase stock				$ 755,500,000	$ 395,500,000
Average price per share (in dollars per share)				$ 25.62
Stock Repurchase Program 2018
Accelerated Share Repurchases [Line Items]
Stock repurchase program, authorized amount							$ 2,000,000,000
Stock repurchased and retired (in shares)	6.0			29.3
Average price per share (in dollars per share)	$ 25.62			$ 25.62
Amount repurchased	$ 0			$ 750,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 1,300,000,000			$ 1,300,000,000
Accelerated Share Repurchase Program
Accelerated Share Repurchases [Line Items]
Stock repurchase program, authorized amount						$ 750,000,000	$ 750,000,000
Payment to repurchase stock		$ 750,000,000
Stock repurchased and retired (in shares)	6.0	23.3		29.3
Amount repurchased				$ 750,000,000
Stock Repurchase Program 2014
Accelerated Share Repurchases [Line Items]
Stock repurchased and retired (in shares)			5.0		13.5
Average price per share (in dollars per share)			$ 28.16		$ 28.85
Amount repurchased			$ 140,000,000		$ 390,000,000

Equity - Components of Accumulated Other Comprehensive (Loss) Income, Net of Tax (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	$ (5.4)
Other comprehensive loss before reclassifications	(20.2)
Amount reclassified from accumulated other comprehensive loss	(4.6)
Other comprehensive income (loss), net	(24.8)
Reclassification of tax effects upon adoption of ASU No. 2018-02	5.7
Balance as of September 30, 2018	(24.5)
Unrealized Gains on Available-for- Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	19.0
Other comprehensive loss before reclassifications	(0.6)
Amount reclassified from accumulated other comprehensive loss	0.9
Other comprehensive income (loss), net	0.3
Reclassification of tax effects upon adoption of ASU No. 2018-02	5.0
Balance as of September 30, 2018	24.3
Unrealized (Losses) Gains on Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	6.0
Other comprehensive loss before reclassifications	(5.9)
Amount reclassified from accumulated other comprehensive loss	(5.5)
Other comprehensive income (loss), net	(11.4)
Reclassification of tax effects upon adoption of ASU No. 2018-02	0.7
Balance as of September 30, 2018	(4.7)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance as of December 31, 2017	(30.4)
Other comprehensive loss before reclassifications	(13.7)
Amount reclassified from accumulated other comprehensive loss	0.0
Other comprehensive income (loss), net	(13.7)
Reclassification of tax effects upon adoption of ASU No. 2018-02	0.0
Balance as of September 30, 2018	$ (44.1)

Employee Benefit Plans - Equity Incentive Plan and Stock Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Number of Shares
Balance at beginning of period (in shares)	0.9
Exercised (in shares)	(0.1)
Expired/canceled (in shares)	(0.7)
Balance at end of period (in shares)	0.1
Weighted Average Exercise Price per Share
Balance at beginning of period (in dollars per share) \| $ / shares	$ 34.41
Exercised (in dollars per share) \| $ / shares	4.20
Expired/canceled (in dollars per share) \| $ / shares	40.34
Balance at end of period (in dollars per share) \| $ / shares	$ 19.80
Weighted average remaining contractual term at end of period	1 year 10 months 25 days
Aggregate intrinsic value at end of period \| $	$ 1.2
Vested and expected-to-vest options at end of period (in shares)	0.1
Vested and expected-to-vest options, weighted average exercise price at end of period (in dollars per share) \| $ / shares	$ 19.80
Vested and expected-to-vest options, weighted average remaining contractual term at end of period	1 year 10 months 25 days
Vested or expected-to-vest options, aggregate intrinsic value at end of period \| $	$ 1.2
Exercisable options at end of period (in shares)	0.1
Exercisable options, weighted average exercise price at end of period (in dollars per share) \| $ / shares	$ 22.24
Exercisable options, weighted average remaining contractual term at end of period	1 year
Exercisable options, aggregate intrinsic value at end of period \| $	$ 0.8
Equity incentive plan 2015
Share-Based Compensation Plans
Number of shares available for future issuance	23.3
Employee stock purchase plan 2008
Share-Based Compensation Plans
Number of shares available for future issuance	8.7

Employee Benefit Plans - Equity Instruments Other Than Options (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended						9 Months Ended
	Jul. 26, 2018	May 02, 2018	Jan. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Weighted Average Grant-Date Fair Value per Share
Cash dividends declared per common stock (in dollars per share)	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.1	$ 0.10	$ 0.10	$ 0.54	$ 0.3
RSUs, RSAs, and PSAs
Number of Shares
Balance at beginning of period (in shares)						19.5				19.5
Balance at end of period (in shares)				18.0						18.0
Weighted Average Grant-Date Fair Value per Share
Balance at beginning of period (in dollars per share)						$ 25.39				$ 25.39
Balance at end of period (in dollars per share)				$ 25.37						$ 25.37
Weighted average remaining contractual term										1 year 1 month 6 days
Aggregate intrinsic value				$ 538.8						$ 538.8
Restricted Stock Units (RSUs)
Number of Shares
Granted (in shares)										6.5
Vested (in shares)										(5.4)
Canceled (in shares)										(1.5)
Weighted Average Grant-Date Fair Value per Share
Granted (in dollars per share)										$ 25.36
Vested (in dollars per share)										25.43
Canceled (in dollars per share)										$ 26.34
Performance goal, number of shares (in shares)				0.1						0.1
Performance shares (PSAs)
Number of Shares
Granted (in shares)										0.7
Vested (in shares)										(1.1)
Canceled (in shares)										(0.7)
Weighted Average Grant-Date Fair Value per Share
Granted (in dollars per share)										$ 24.43
Vested (in dollars per share)										24.14
Canceled (in dollars per share)										$ 24.39
Performance goal, number of shares (in shares)				0.4						0.4
Number of shares modified										2.0
Incremental compensation cost resulting from the modifications										$ 6.3
Minimum \| Restricted Stock Units (RSUs)
Weighted Average Grant-Date Fair Value per Share
Performance goal, number of shares (in shares)				0.0						0.0
Minimum \| Performance shares (PSAs)
Weighted Average Grant-Date Fair Value per Share
Performance goal, number of shares (in shares)				0.0						0.0
Maximum \| Restricted Stock Units (RSUs)
Weighted Average Grant-Date Fair Value per Share
Performance goal, number of shares (in shares)				0.3						0.3
Maximum \| Performance shares (PSAs)
Weighted Average Grant-Date Fair Value per Share
Performance goal, number of shares (in shares)				0.7						0.7

Employee Benefit Plans - Employee Stock Purchase Plan (Details) shares in Millions		3 Months Ended		9 Months Ended
	Nov. 06, 2017 period	Sep. 30, 2018 $ / shares shares	Sep. 30, 2017 $ / shares shares	Sep. 30, 2018 $ / shares shares	Sep. 30, 2017 $ / shares shares
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
ESPP offering period duration	24 months
ESPP, number of purchase period \| period	4
ESPP. purchase period	6 months
ESPP, purchase price of common stock	85.00%
Employee stock purchase plan 2008
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Shares purchased (in shares) \| shares		1.2	1.2	2.5	2.7
Average exercise price per share (in dollars per share) \| $ / shares		$ 22.39	$ 22.79	$ 22.31	$ 20.83

Employee Benefit Plans - Share Based Compensation by Cost and Expense Categories (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	$ 53.2	$ 45.0	$ 180.2	$ 151.1
Stock options
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	0.1	0.2	0.3	0.5
RSUs, RSAs, and PSAs
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	48.2	41.0	165.8	138.9
ESPP
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	4.9	3.8	14.1	11.7
Cost of revenues - Product
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	1.5	1.5	5.1	3.8
Cost of revenues - Service
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	4.5	3.9	14.2	13.5
Research and development
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	28.1	18.5	101.8	67.4
Sales and marketing
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	12.9	13.7	40.4	45.3
General and administrative
Stock Based Compensation Expense Recorded in Cost and Expense Categories
Share-based compensation expense	$ 6.2	$ 7.4	$ 18.7	$ 21.1

Employee Benefit Plans - Share Based Compensation by Share Based Payment Award Types (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Unrecognized compensation cost	$ 320.2
Unrecognized compensation, weighted average recognition period	1 year 7 months 6 days

Segments - Revenue by Product (Details) $ in Millions	3 Months Ended		9 Months Ended
Segments - Revenue by Product (Details) $ in Millions	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment			1
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Product
Segment Reporting Information [Line Items]
Total net revenues	794.7	869.7	2,330.4	2,615.8
Routing
Segment Reporting Information [Line Items]
Total net revenues	496.4	585.8	1,395.1	1,679.9
Switching
Segment Reporting Information [Line Items]
Total net revenues	221.1	212.6	705.9	730.2
Security
Segment Reporting Information [Line Items]
Total net revenues	77.2	71.3	229.4	205.7
Service
Segment Reporting Information [Line Items]
Total net revenues	$ 385.1	$ 388.1	$ 1,136.1	$ 1,171.9

Segments - Revenues by Customer Vertical (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Cloud
Segment Reporting Information [Line Items]
Total net revenues	250.0	344.9	798.1	1,056.1
Service Provider
Segment Reporting Information [Line Items]
Total net revenues	543.6	576.9	1,546.8	1,707.8
Enterprise
Segment Reporting Information [Line Items]
Total net revenues	$ 386.2	$ 336.0	$ 1,121.6	$ 1,023.8

Segments - Geographic (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Segments - Geographic (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total net revenues	$ 1,179.8	$ 1,257.8	$ 3,466.5	$ 3,787.7
Total Americas
Segment Reporting Information [Line Items]
Total net revenues	643.1	729.2	1,906.4	2,241.6
United States
Segment Reporting Information [Line Items]
Total net revenues	597.1	668.8	1,754.2	2,076.0
Other
Segment Reporting Information [Line Items]
Total net revenues	46.0	60.4	152.2	165.6
Europe, Middle East, and Africa
Segment Reporting Information [Line Items]
Total net revenues	329.9	298.6	946.8	871.3
Asia Pacific
Segment Reporting Information [Line Items]
Total net revenues	$ 206.8	$ 230.0	$ 613.3	$ 674.8

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income before income taxes	$ 152.0	$ 225.8	$ 344.3	$ 611.6
Income tax (benefit) provision	$ (71.8)	$ 60.1	$ (30.4)	$ 157.3
Effective tax (benefit) rate	(47.20%)	26.60%	(8.80%)	25.70%
Federal statutory rate	21.00%		21.00%
Recognition of previously unrecognized tax benefits	$ 67.6		$ 67.6
Unrecognized tax benefits, interest	8.4		8.4
Reduction of expected tax liabilities, change in accounting method for tax recognition of deferred product revenue	33.2		33.2
Unrecognized tax benefits	205.0		205.0
Unrecognized tax benefits, if recognized would affect the effective tax rate	183.3		183.3
Unrecognized tax benefits could decrease up to	$ 7.9		$ 7.9

Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income	$ 223.8	$ 165.7	$ 374.7	$ 454.3
Denominator:
Weighted-average shares used to compute basic net income per share (in shares)	346.2	378.3	350.1	380.0
Dilutive effect of employee stock awards (in shares)	4.3	4.4	5.1	6.5
Weighted-average shares used to compute diluted net income per share (in shares)	350.5	382.7	355.2	386.5
Net income per share
Basic (in dollars per share)	$ 0.65	$ 0.44	$ 1.07	$ 1.20
Diluted, (in dollars per share)	$ 0.64	$ 0.43	$ 1.05	$ 1.18
Anti-dilutive shares (in shares)	4.2	1.0	5.0	1.2

Commitments and Contingencies - Commitments (Details) $ in Millions	Sep. 30, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Purchase obligation	$ 610.9
Excess purchase commitments and obsolete materials liability	$ 23.6

Commitments and Contingencies - Guarantees (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Indemnification Agreement
Guarantor Obligations [Line Items]
Guarantor obligations, current carrying value	$ 12.0	$ 20.4

Commitments and Contingencies - Investigations (Details) $ in Millions	Sep. 30, 2018 USD ($)
Investigations by U.S. Securities and Exchange Commission (SEC) and U.S. Department of Justice (DOJ) \| Pending Litigation
Loss Contingencies [Line Items]
Estimated legal reserve	$ 12.0

Subsequent Events (Details) - $ / shares					3 Months Ended						9 Months Ended
Subsequent Events (Details) - $ / shares	Oct. 23, 2018	Jul. 26, 2018	May 02, 2018	Jan. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Cash dividends declared per common stock (in dollars per share)		$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.1	$ 0.10	$ 0.10	$ 0.54	$ 0.3
Subsequent Event
Subsequent Event [Line Items]
Cash dividends declared per common stock (in dollars per share)	$ 0.18