CDW (CDW) 10-Q 2 Nov 20 2020 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 29, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-35985
Entity Central Index Key	0001402057
Current Fiscal Year End Date	--12-31
Entity Registrant Name	CDW CORP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-0273989
Entity Address, Address Line One	75 Tri-State International
Entity Address, City or Town	Lincolnshire
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60069
City Area Code	847
Local Phone Number	465-6000
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	CDW
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		142,988,211
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 1,249.5	$ 154
Accounts receivable, net of allowance for credit losses of $32.7 and $7.9, respectively	3,267.7	3,002.2
Merchandise inventory	648.1	611.2
Miscellaneous receivables	404.1	395.1
Prepaid expenses and other	190.2	171.6
Total current assets	5,759.6	4,334.1
Operating lease right-of-use assets	133.5	131.8
Property and equipment, net	268	363.1
Goodwill	2,573.4	2,553
Other intangible assets, net	461.8	594.1
Other assets	27.4	23.3
Total Assets	9,223.7	7,999.4
Current liabilities:
Accounts payable-trade	1,922	1,835
Accounts payable-inventory financing	661.2	429.9
Current maturities of long-term debt	72.3	34.1
Contract liabilities	246.8	252.2
Accrued expenses and other current liabilities:
Compensation	216.4	212.3
Advertising	157.7	147.9
Sales and income taxes	68.8	88.6
Other	491.4	491.4
Total current liabilities	3,836.6	3,491.4
Long-term liabilities:
Debt	3,858.6	3,283.2
Deferred income taxes	63.1	62.4
Operating lease liabilities	151.5	131.1
Other liabilities	75.4	71
Total long-term liabilities	4,148.6	3,547.7
Stockholders' equity:
Preferred stock, $0.01 par value, 100.0 shares authorized; no shares issued or outstanding for both periods	0	0
Common stock, $0.01 par value, 1,000.00 shares authorized; 142.8 and 143.0 shares outstanding, respectively	1.4	1.4
Paid-in capital	3,161.8	3,095.3
Accumulated deficit	(1,794)	(2,018.6)
Accumulated other comprehensive loss	(130.7)	(117.8)
Total stockholders' equity	1,238.5	960.3
Total Liabilities and Stockholders' Equity	$ 9,223.7	$ 7,999.4

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Allowance for credit loss, current	$ 32.7	$ 7.9
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	100,000,000	100,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares outstanding (in shares)	142,800,000	143,000,000

Consolidated Statements Of Oper

Consolidated Statements Of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Net sales	$ 4,756.4	$ 4,907.7	$ 13,511.3	$ 13,495.5
Cost of sales	3,930.9	4,091.2	11,182.1	11,233.1
Gross profit	825.5	816.5	2,329.2	2,262.4
Selling and administrative expenses	507.7	495.9	1,482.2	1,412.6
Operating income	317.8	320.6	847	849.8
Interest expense, net	(40.2)	(42.3)	(117.8)	(121.1)
Other expense, net	(27.5)	(17.4)	(21.9)	(15)
Income before income taxes	250.1	260.9	707.3	713.7
Income tax expense	(56.9)	(59.2)	(157.1)	(162.5)
Net income	$ 193.2	$ 201.7	$ 550.2	$ 551.2
Net income per common share:
Basic (in dollars per share)	$ 1.36	$ 1.39	$ 3.86	$ 3.78
Diluted (in dollars per share)	$ 1.33	$ 1.37	$ 3.80	$ 3.72
Weighted-average common shares outstanding:
Basic (in shares)	142.7	144.5	142.6	145.7
Diluted (in shares)	144.8	147.2	144.7	148.2

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 193.2	$ 201.7	$ 550.2	$ 551.2
Other comprehensive income (loss):
Unrealized loss from hedge accounting, net of tax	(0.4)	(0.4)	(0.6)	(12.8)
Reclassification of hedge accounting loss to net income, net of tax	1.6	0.3	4.1	2
Foreign currency translation, net of tax	19.7	(14.6)	(16.4)	(12.7)
Other comprehensive income (loss)	20.9	(14.7)	(12.9)	(23.5)
Comprehensive income	$ 214.1	$ 187	$ 537.3	$ 527.7

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, AdjustmentAccumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		147.7
Beginning balance at Dec. 31, 2018	$ 975.2	$ 1.5	$ 2,996.9	$ (1,892.6)	$ (130.6)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	551.2			551.2
Equity-based compensation expense	36.9		36.9
Stock option exercises (in shares)		1
Stock option exercises	27.6		27.6
Coworker Stock Purchase Plan	11.2		11.2
Repurchases of common stock (in shares)		(4.8)
Repurchases of common stock	(493.3)	$ (0.1)		(493.2)
Dividends paid	(128.9)		0.6	(129.5)
Incentive compensation plan stock withheld for taxes	(21.3)			(21.3)
Foreign currency translation	(12.7)				(12.7)
Unrealized (loss) gain from hedge accounting	(12.8)				(12.8)
Reclassification of hedge accounting loss to net income	2				2
Ending balance (in shares) at Sep. 30, 2019		143.9
Ending balance at Sep. 30, 2019	935.1	$ 1.4	3,073.2	(1,985.4)	(154.1)
Beginning balance (in shares) at Jun. 30, 2019		145
Beginning balance at Jun. 30, 2019	936.1	$ 1.5	3,047.6	(1,973.6)	(139.4)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	201.7			201.7
Equity-based compensation expense	12.9		12.9
Stock option exercises (in shares)		0.3
Stock option exercises	8.6		8.6
Coworker Stock Purchase Plan (in shares)		0
Coworker Stock Purchase Plan	3.9		3.9
Repurchases of common stock (in shares)		(1.4)
Repurchases of common stock	(161.1)	$ (0.1)		(161)
Dividends paid	(42.6)		0.2	(42.8)
Incentive compensation plan stock withheld for taxes	(9.7)			(9.7)
Foreign currency translation	(14.6)				(14.6)
Unrealized (loss) gain from hedge accounting	(0.4)				(0.4)
Reclassification of hedge accounting loss to net income	0.3				0.3
Ending balance (in shares) at Sep. 30, 2019		143.9
Ending balance at Sep. 30, 2019	935.1	$ 1.4	3,073.2	(1,985.4)	(154.1)
Beginning balance (in shares) at Dec. 31, 2019		143
Beginning balance at Dec. 31, 2019	960.3	$ 1.4	3,095.3	(2,018.6)	(117.8)	$ 0.5	$ 0.5
Shareholders' Equity (Deficit) [Roll Forward]
Net income	550.2			550.2
Equity-based compensation expense	26		26
Stock option exercises (in shares)		0.9
Stock option exercises	26.9		26.9
Coworker Stock Purchase Plan	12.8		12.8
Repurchases of common stock (in shares)		(1.1)
Repurchases of common stock	(140.8)	$ 0		(140.8)
Dividends paid	(162.4)		0.8	(163.2)
Incentive compensation plan stock withheld for taxes	(22.1)			(22.1)
Foreign currency translation	(16.4)				(16.4)
Unrealized (loss) gain from hedge accounting	(0.6)				(0.6)
Reclassification of hedge accounting loss to net income	4.1				4.1
Ending balance (in shares) at Sep. 30, 2020		142.8
Ending balance at Sep. 30, 2020	1,238.5	$ 1.4	3,161.8	(1,794)	(130.7)
Beginning balance (in shares) at Jun. 30, 2020		142.6
Beginning balance at Jun. 30, 2020	1,055.6	$ 1.4	3,138.3	(1,932.5)	(151.6)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	193.2			193.2
Equity-based compensation expense	11.6		11.6
Stock option exercises (in shares)		0.2
Stock option exercises	7.1		7.1
Coworker Stock Purchase Plan	4.5		4.5
Dividends paid	(54.2)		0.3	(54.5)
Incentive compensation plan stock withheld for taxes	(0.2)			(0.2)
Foreign currency translation	19.7				19.7
Unrealized (loss) gain from hedge accounting	(0.4)				(0.4)
Reclassification of hedge accounting loss to net income	1.6				1.6
Ending balance (in shares) at Sep. 30, 2020		142.8
Ending balance at Sep. 30, 2020	$ 1,238.5	$ 1.4	$ 3,161.8	$ (1,794)	$ (130.7)

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Statement of Stockholders' Equity [Abstract]
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Dividends (in dollars per share)	$ 0.380	$ 0.295	$ 1.140	$ 0.885

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 550.2	$ 551.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	349	197.5
Equity-based compensation expense	26	37.7
Deferred income taxes	(2.5)	(33.5)
Provision for credit losses	30.4	2.1
Other	38.4	23.1
Changes in assets and liabilities:
Accounts receivable	(304.9)	(171.8)
Merchandise inventory	(34.2)	(151.1)
Other assets	(10.3)	(82.2)
Accounts payable-trade	106.8	264
Other liabilities	(10.5)	45.3
Net cash provided by operating activities	738.4	682.3
Cash flows used in investing activities:
Capital expenditures	(133.6)	(75)
Acquisition of business, net of cash acquired	(38.5)	(75)
Net cash used in investing activities	(172.1)	(150)
Cash flows from financing activities:
Proceeds from borrowings under revolving credit facility	1,024	1,860.5
Repayments of borrowings under revolving credit facility	(1,075)	(1,834.5)
Proceeds from issuance of long-term debt	1,300	600
Payments to extinguish long-term debt	(622.5)	(538.1)
Net change in accounts payable-inventory financing	232.5	(17.4)
Repurchases of common stock	(140.8)	(493.3)
Payment of incentive compensation plan withholding taxes	(22.1)	(21.3)
Dividend payments	(162.4)	(128.9)
Other	(2)	4.5
Net cash provided by (used in) financing activities	531.7	(568.5)
Effect of exchange rate changes on cash and cash equivalents	(2.5)	(2.7)
Net increase (decrease) in cash and cash equivalents	1,095.5	(38.9)
Cash and cash equivalents—beginning of period	154	205.8
Cash and cash equivalents—end of period	1,249.5	166.9
Supplementary disclosure of cash flow information:
Interest paid	(90.5)	(124.8)
Income taxes paid, net	$ (196.4)	$ (203)

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Description of Business and Summary of Significant Accounting Policies	Description of Business and Summary of Significant Accounting Policies Description of Business CDW Corporation ("Parent"), a Fortune 500 company and member of the S&P 500 Index, is a market-leading provider of integrated information technology ("IT") solutions to small, medium and large business, government, education and healthcare customers in the United States ("US"), the United Kingdom ("UK") and Canada. The Company's offerings range from discrete hardware and software products to integrated IT solutions such as mobility, security, data center optimization, cloud computing, virtualization and collaboration. Throughout this report, the terms the "Company" and "CDW" refer to Parent and its 100% owned subsidiaries. Parent has two 100% owned subsidiaries, CDW LLC and CDW Finance Corporation. CDW LLC is an Illinois limited liability company that, together with its 100% owned subsidiaries, holds all material assets and conducts all business activities and operations of the Company. CDW Finance Corporation is a Delaware corporation formed for the sole purpose of acting as co-issuer of certain debt obligations and does not hold any material assets or engage in any business activities or operations. Basis of Presentation The accompanying unaudited interim Consolidated Financial Statements as of September 30, 2020 and for the three and nine months ended September 30, 2020 and 2019 (the "Consolidated Financial Statements") have been prepared in conformity with accounting principles generally accepted in the United States of America ("US GAAP") and the rules and regulations of the US Securities and Exchange Commission (the "SEC") for interim financial statements. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with US GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. These Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and the notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019 (the "December 31, 2019 Consolidated Financial Statements"). The significant accounting policies used in preparing these Consolidated Financial Statements were applied on a basis consistent with those reflected in the December 31, 2019 Consolidated Financial Statements. In the opinion of management, the Consolidated Financial Statements contain all adjustments (consisting of a normal, recurring nature) necessary to present fairly the Company's financial position, results of operations, comprehensive income, cash flows and changes in stockholders' equity as of the dates and for the periods indicated. The unaudited results of operations for such interim periods reported are not necessarily indicative of results for the full year. Reclassifications Certain prior period amounts have been reclassified to conform with current period presentation. Principles of Consolidation The Consolidated Financial Statements include the accounts of Parent and its 100% owned subsidiaries. All intercompany transactions and accounts are eliminated in consolidation. Use of Estimates The preparation of the Consolidated Financial Statements in accordance with US GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the Consolidated Financial Statements and the reported amounts of revenue and expenses during the reported periods. The Company bases its estimates on historical experience and on various other assumptions that management believes are reasonable under the circumstances including management’s current assumptions with respect to implications of the novel coronavirus (“COVID-19”) pandemic, the results of which form the basis for making judgments about carrying values of assets and liabilities that are not readily apparent from other sources. Actual results and outcomes could differ from those estimates. The notes to the Consolidated Financial Statements contained in the December 31, 2019 Consolidated Financial Statements include a discussion of the Company's significant accounting policies and estimates. Except as noted within Note 2 (Recent Accounting Pronouncements) for the adoption of Accounting Standards Update ("ASU") 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("Topic 326"), there have been no changes to the Company's significant accounting policies and estimates during the nine months ended September 30, 2020. Accounts Receivable The Company estimates an allowance for credit losses related to accounts receivable for future expected credit losses by using relevant information such as historical information, current conditions, and reasonable and supportable forecasts. The allowance is measured on a pool basis when similar risk characteristics exist, and a loss-rate for each pool is determined using historical credit loss experience as the basis for the estimation of expected credit losses. Adjustments to historical loss information are made for differences in current conditions as well as changes in forecasted macroeconomic conditions, such as changes in the unemployment rate or gross domestic product growth rate. The Company has typically experienced a higher loss-rate experience with customers in pools associated with the Company's Corporate and Small Business segments, as compared to the pools associated with the Public segment. During the nine months ended September 30, 2020, the Company recognized an allowance of $30 million to reflect the forecasted credit deterioration due to the COVID-19 pandemic, which considered the customer makeup and overall size of the Company's pools, the impacts experienced to date and the impacts from the last significant economic downturn in 2008-2009. Due to the higher inherent risk in the pools associated with the Company's Corporate and Small Business segments, and the overall size of certain pools within the Public segment, the majority of the additional allowance relates to these segments. As the overall impact and duration of the COVID-19 pandemic remains uncertain, the Company's estimates and assumptions may evolve as conditions change. Advertising Advertising costs are generally charged to expense in the period incurred and recorded in Selling and administrative expenses in the Consolidated Statements of Operations. During the three months ended September 30, 2020 and 2019, the Company had advertising costs of $47 million and $51 million, respectively. During the nine months ended September 30, 2020 and 2019, the Company had advertising costs of $140 million and $143 million, respectively.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2020
Accounting Standards Update and Change in Accounting Principle [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Reference Rate Reform In March 2020, the Financial Accounting Standards Board issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting. This ASU temporarily provides optional expedients and exceptions for applying existing guidance to contract modifications, hedging relationships and other transactions that are expected to be affected by reference rate reform. This ASU was effective upon its issuance and will remain in effect for all contract modifications and hedging relationships entered into through December 31, 2022. The adoption of this ASU along with the related expedients did not have an impact to the Company’s Consolidated Financial Statements. Measurement of Credit Losses on Financial Instruments On January 1, 2020, the Company adopted and applied Topic 326 using the modified retrospective approach. Topic 326 introduced a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables, which is reflected in the Company’s policies. The adoption of Topic 326, as well as the adjustment to retained earnings for the cumulative effect, was not significant to the Company's Consolidated Financial Statements.

Inventory Financing Agreements

Inventory Financing Agreements	9 Months Ended
	Sep. 30, 2020
Inventory Financing Agreements [Abstract]
Inventory Financing Agreements	Inventory Financing AgreementsThe Company has entered into agreements with certain financial intermediaries to facilitate the purchase of inventory from various suppliers under certain terms and conditions, as described below. These amounts are classified separately as Accounts payable-inventory financing on the Consolidated Balance Sheets. The Company does not incur any interest expense associated with these agreements as balances are paid when they are due. Amounts included in Accounts payable-inventory financing are as follows: September 30, 2020 December 31, 2019 Revolving Loan inventory financing agreement (1) $ 608.9 $ 379.1 Other inventory financing agreements 52.3 50.8 Accounts payable-inventory financing $ 661.2 $ 429.9 (1) The senior secured asset-based revolving credit facility includes an inventory floorplan sub-facility that enables the Company to maintain an inventory financing agreement with a financial intermediary to facilitate the purchase of inventory from certain vendors on more favorable terms than offered directly by the vendors.

Contract Liabilities and Perfor

Contract Liabilities and Performance Obligations	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Contract Liabilities and Performance Obligations	Contract Liabilities and Performance Obligations The Company's contract liabilities consist of payments received from customers, or such consideration that is contractually due, in advance of providing the product or performing services. The Company's contract liabilities are reported in a net position on a contract-by-contract basis at the end of each reporting period. As of September 30, 2020 and December 31, 2019, the contract liability balance was $247 million and $252 million, respectively. During the nine months ended September 30, 2020 and 2019, the Company recognized revenue of $157 million and $117 million, respectively, related to its contract liabilities. A contract's transaction price is allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The following table represents the total transaction price for the remaining performance obligations as of September 30, 2020 related to noncancelable contracts longer than 12 months in duration that is expected to be recognized over future periods. Within 1 Year Years 1-2 Years 2-3 Thereafter Remaining performance obligations $ 32.2 $ 20.6 $ 6.9 $ 0.3

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2020
Financial Instruments [Abstract]
Financial Instruments	Financial Instruments The Company's indebtedness creates interest rate risk on its variable-rate debt. The Company uses derivative financial instruments to manage its exposure to interest rate risk. The Company does not hold or issue derivative financial instruments for trading or speculative purposes. The Company has interest rate cap agreements that entitle it to payments from the counterparty of the amount, if any, by which three-month London Interbank Offered Rate ("LIBOR") exceeds the strike rates of the caps during the agreement period in exchange for an upfront premium. During 2020, the Company did not enter into interest rate cap agreements. As of September 30, 2020 and December 31, 2019, the Company had interest rate cap agreements with a fair value of less than $1 million, which were classified within Other assets on the Consolidated Balance Sheets. The total notional value of the interest rate cap agreements was $2.8 billion as of September 30, 2020 and December 31, 2019, of which $1.4 billion mature at December 31, 2020 and December 31, 2022, respectively. The fair values of the Company's interest rate cap agreements are classified as Level 2 in the fair value hierarchy. The valuation of the interest rate cap agreements is derived by using a discounted cash flow analysis on the expected cash receipts that would occur if variable interest rates rise above the strike rates of the caps. This analysis reflects the contractual terms of the interest rate cap agreements, including the period to maturity, and uses observable market-based inputs, including LIBOR curves and implied volatilities. The Company also incorporates insignificant credit valuation adjustments to appropriately reflect the respective counterparty's nonperformance risk in the fair value measurements. The counterparty credit spreads are based on publicly available credit information obtained from a third-party credit data provider. For additional information, see Note 6 (Long-Term Debt). The interest rate cap agreements are designated as cash flow hedges. The changes in the fair value of derivatives that qualify as cash flow hedges are recorded in Accumulated other comprehensive loss ("AOCL") and are subsequently reclassified into Interest expense in the period when the hedged forecasted transaction affects earnings. The following tables provide the activity in AOCL, net of tax, for the three and nine months ended September 30, 2020 and September 30, 2019. Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Change in fair value recorded to AOCL $ (0.4) $ (0.4) $ (0.6) $ (12.8) Reclassification from AOCL to Interest expense, net $ 1.6 $ 0.3 $ 4.1 $ 2.0 The Company expects to reclassify $5 million from AOCL to earnings within Interest expense, net during the next 12 months.

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt As of September 30, 2020 As of December 31, 2019 Maturity Date Interest Rate Amount Interest Rate Amount Credit Facilities CDW UK revolving credit facility (1) July 2021 — % $ — — % $ — Senior secured asset-based revolving credit facility March 2022 — % — 5.000 % 51.0 Total credit facilities — 51.0 Term Loans CDW UK term loan (1) August 2021 1.464 % 53.0 2.190 % 61.0 Senior secured term loan facility October 2026 1.900 % 1,427.1 3.550 % 1,438.3 Total term loans 1,480.1 1,499.3 Unsecured Senior Notes Senior notes due 2024 December 2024 5.500 % 575.0 5.500 % 575.0 Senior notes due 2025 May 2025 4.125 % 600.0 — % — Senior notes due 2025 September 2025 — % — 5.000 % 600.0 Senior notes due 2028 April 2028 4.250 % 600.0 4.250 % 600.0 Senior notes due 2029 February 2029 3.250 % 700.0 — % — Total unsecured senior notes 2,475.0 1,775.0 Other long-term obligations 4.4 12.6 Unamortized deferred financing fees (28.6) (20.6) Current maturities of long-term debt (72.3) (34.1) Total long-term debt $ 3,858.6 $ 3,283.2 (1) British pound-denominated debt facilities. As of September 30, 2020, the Company is in compliance with the covenants under the various credit agreements and indentures. Credit Facilities The Company has a variable rate CDW UK revolving credit facility that is denominated in British pounds. As of September 30, 2020, the Company could have borrowed up to an additional £50 million ($65 million) under the CDW UK revolving credit facility. The Company also has a variable rate senior secured asset-based revolving credit facility (the "Revolving Loan") that is denominated in US dollars. The Revolving Loan is used by the Company for borrowings, issuances of letters of credit and floorplan financing. As of September 30, 2020, the Revolving Loan had less than $1 million of undrawn letters of credit, $594 million reserved for the floorplan sub-facility and a borrowing base of $2.4 billion, which is based on the amount of eligible inventory and accounts receivable balances as of August 31, 2020. As of September 30, 2020, the Company could have borrowed up to an additional $856 million under the Revolving Loan. The Revolving Loan is collateralized by a first priority interest in inventory (excluding inventory to the extent collateralized under the inventory financing arrangements as described in Note 3 (Inventory Financing Agreements)), deposits and accounts receivable, and by a second priority interest in substantially all other US assets. Term Loans The CDW UK term loan has a variable interest rate with the remaining principal amount due at the maturity date. The CDW UK term loan agreement imposes restrictions on CDW UK's ability to transfer funds to the Company through the payment of dividends, repayment of intercompany loans, advances or subordinated debt that require, among other things, the maintenance of a minimum net leverage ratio. As of September 30, 2020, the amount of restricted payment capacity under the CDW UK term loan was £173 million ($223 million). The senior secured term loan facility (the "Term Loan") has a variable interest rate, which has effectively been capped through the use of interest rate caps (see Note 5 (Financial Instruments)). The interest rate disclosed in the table above represents the variable interest rates in effect for September 30, 2020 and December 31, 2019, respectively. The Company is required to pay quarterly principal installments of $4 million with the remaining principal amount due at the maturity date. As of September 30, 2020, the amount of CDW's restricted payment capacity under the Term Loan was $2.1 billion. The Term Loan is collateralized by a second priority interest in substantially all inventory (excluding inventory to the extent collateralized under the inventory financing arrangements as described in Note 3 (Inventory Financing Agreements), deposits and accounts receivable, and by a first priority interest in substantially all other US assets. Unsecured Senior Notes The senior notes have fixed interest rates, for which interest is paid semi-annually. On April 21, 2020, CDW completed the issuance of $600 million aggregate principal amount of 4.125% Senior Notes due 2025 at par. The 2025 Senior Notes will mature on May 1, 2025 and bear interest of 4.125% per annum, payable semi-annually on May 1 and November 1 of each year, commencing November 1, 2020. On August 13, 2020, CDW completed the issuance of $700 million aggregate principal amount of 3.25% Senior Notes due 2029 at par. The 2029 Senior Notes will mature on February 15, 2029 and bear interest of 3.25% per annum, payable semi-annually on February 15 and August 15 of each year, commencing February 15, 2021. The net proceeds from the issuance were primarily used to redeem all of the remaining $600 million aggregate principal amount of the 5.000% Senior Notes due September 2025 at a redemption price of 103.75% of the principal amount redeemed, plus accrued and unpaid interest to the date of redemption, to pay fees and expenses related to the issuance and redemption, and for general corporate purposes. Fair Value The fair values of the Senior Notes were estimated using quoted market prices for identical liabilities that are traded in over-the-counter secondary markets that are not considered active. The fair value of the Term Loan was estimated using dealer quotes for identical liabilities in markets that are not considered active. The Senior Notes, Term Loan and CDW UK term loan are classified as Level 2 within the fair value hierarchy. The carrying value of the Revolving Loan and CDW UK revolving credit facility approximate fair value if there are outstanding borrowings. The approximate fair values and related carrying values of the Company's long-term debt, including current maturities and excluding unamortized discount and unamortized deferred financing fees, are as follows: September 30, 2020 December 31, 2019 Fair value $ 4,026.1 $ 3,447.5 Carrying value 3,959.5 3,337.9

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act ("CARES Act") was enacted into law. The primary impact to the Company’s financial statements as a result of the CARES Act was the deferral of US corporate income tax payments from the second quarter of 2020 to July 2020, as well as the deferral of employer related payroll tax payments from the second, third and fourth quarters of 2020 with 50% to be paid in the fourth quarter of 2021 and the remaining 50% to be paid in the fourth quarter of 2022. Income tax expense was $57 million and $59 million for the three months ended September 30, 2020 and 2019, respectively. The effective tax rate, expressed by calculating the income tax expense as a percentage of Income before income taxes, was 22.7% for both the three months ended September 30, 2020 and 2019. The effective tax rates differed from the US statutory rate of 21.0% for the three months ended September 30, 2020 primarily due to state and local income taxes and a discrete deferred tax expense as a result of an increase in the UK corporate tax rate, partially offset by excess tax benefits on equity-based compensation. The effective tax rate differed from the US statutory rate of 21.0% for the three months ended September 30, 2019 primarily due to state and local income taxes, partially offset by excess tax benefits on equity-based compensation. Income tax expense was $157 million and $163 million for the nine months ended September 30, 2020 and 2019, respectively. The effective tax rate, expressed by calculating the income tax expense as a percentage of Income before income taxes, was 22.2% for the nine months ended September 30, 2020 and differed from the US federal statutory rate of 21.0% with state and local income taxes and a discrete deferred tax expense as a result of an increase in the UK corporate tax rate being largely offset by excess tax benefits on equity-based compensation. The effective tax rate for the nine months ended September 30, 2019 was 22.8% and differed from the US federal statutory rate of 21.0% primarily due to state and local income taxes, partially offset by excess tax benefits on equity-based compensation and a discrete tax benefit related to CDW Canada's acquisition of Scalar Decisions Inc. ("Scalar") in 2019.

Earnings per Share

Earnings per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings per Share	Earnings Per Share The numerator for both basic and diluted earnings per share is Net income. The denominator for basic earnings per share is the weighted-average shares outstanding during the period. A reconciliation of basic weighted-average shares outstanding to diluted weighted-average shares outstanding is as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic weighted-average shares outstanding 142.7 144.5 142.6 145.7 Effect of dilutive securities (1) 2.1 2.7 2.1 2.5 Diluted weighted-average shares outstanding (2) 144.8 147.2 144.7 148.2 (1) The dilutive effect of outstanding stock options, restricted stock units, restricted stock, performance share units and Coworker Stock Purchase Plan units is reflected in the diluted weighted-average shares outstanding using the treasury stock method. (2) There were fewer than 0.1 million potential common shares excluded from diluted weighted-average shares outstanding for both the three and nine months ended September 30, 2020 and 2019 as their inclusion would have had an anti-dilutive effect.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Company is party to various legal proceedings that arise in the ordinary course of its business, which include commercial, intellectual property, employment, tort and other litigation matters. The Company is also subject to audit by federal, state, international, national, provincial and local authorities, and by various partners, group purchasing organizations and customers, including government agencies, relating to purchases and sales under various contracts. In addition, the Company is subject to indemnification claims under various contracts. From time to time, certain customers of the Company file voluntary petitions for reorganization or liquidation under the US bankruptcy laws or similar laws of the jurisdictions for the Company's business activities outside of the US. In such cases, certain pre-petition payments received by the Company could be considered preference items and subject to return to the bankruptcy administrator. As of September 30, 2020, the Company does not believe that there is a reasonable possibility that any material loss exceeding the amounts already recognized for these proceedings and matters, if any, has been incurred. However, the ultimate resolutions of these proceedings and matters are inherently unpredictable. As such, the Company's consolidated financial statements could be adversely affected in any particular period by the unfavorable resolution of one or more of these proceedings or matters.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has three reportable segments: Corporate, which is comprised primarily of US private sector business customers with more than 250 employees, Small Business, which primarily serves US private sector business customers with up to 250 employees, and Public, which is comprised of government agencies and education and healthcare institutions in the US. The Company has two other operating segments: CDW UK and CDW Canada, both of which do not meet the reportable segment quantitative thresholds and, accordingly, are included in an all other category ("Other"). Headquarters function costs that are not allocated to the segments are included under the heading of "Headquarters" in the tables below. Information about the Company's segments is as follows: Corporate Small Business Public Other Headquarters Total Three Months Ended September 30, 2020 Net sales $ 1,660.0 $ 337.0 $ 2,293.8 $ 465.6 $ — $ 4,756.4 Operating income (loss) 128.5 24.3 196.1 18.7 (49.8) 317.8 Depreciation and amortization expense (22.4) (5.6) (77.2) (8.4) (18.8) (132.4) Three Months Ended September 30, 2019 Net sales $ 1,913.5 $ 386.2 $ 2,100.9 $ 507.1 $ — $ 4,907.7 Operating income (loss) 138.9 27.2 168.4 21.9 (35.8) 320.6 Depreciation and amortization expense (21.7) (5.6) (15.0) (7.9) (18.0) (68.2) Corporate Small Business Public Other Headquarters Total Nine Months Ended September 30, 2020 Net sales $ 5,128.5 $ 1,030.6 $ 5,841.2 $ 1,511.0 $ — $ 13,511.3 Operating income (loss) 378.9 72.6 468.4 49.9 (122.8) 847.0 Depreciation and amortization expense (66.8) (17.0) (184.0) (24.3) (56.9) (349.0) Nine Months Ended September 30, 2019 Net sales $ 5,533.6 $ 1,119.2 $ 5,271.7 $ 1,571.0 $ — $ 13,495.5 Operating income (loss) 430.8 78.2 373.9 66.6 (99.7) 849.8 Depreciation and amortization expense (64.8) (16.8) (41.4) (23.1) (51.4) (197.5) Geographic Areas and Revenue Mix Three Months Ended September 30, 2020 Corporate Small Business Public Other Total Geography (1) United States $ 1,658.4 $ 337.0 $ 2,293.8 $ 6.1 $ 4,295.3 Rest of World 1.6 — — 459.5 461.1 Total Net sales 1,660.0 337.0 2,293.8 465.6 4,756.4 Major Product and Services Hardware 1,252.0 281.7 1,917.8 340.7 3,792.2 Software 284.9 43.3 304.7 73.2 706.1 Services 107.1 7.0 63.8 49.5 227.4 Other (2) 16.0 5.0 7.5 2.2 30.7 Total Net sales 1,660.0 337.0 2,293.8 465.6 4,756.4 Sales by Channel Corporate 1,660.0 — — — 1,660.0 Small Business — 337.0 — — 337.0 Government — — 847.7 — 847.7 Education — — 1,078.2 — 1,078.2 Healthcare — — 367.9 — 367.9 Other — — — 465.6 465.6 Total Net sales 1,660.0 337.0 2,293.8 465.6 4,756.4 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 1,474.2 313.9 2,080.3 407.7 4,276.1 Transferred at a point in time where CDW is agent 121.3 20.9 89.3 13.9 245.4 Transferred over time where CDW is principal 64.5 2.2 124.2 44.0 234.9 Total Net sales $ 1,660.0 $ 337.0 $ 2,293.8 $ 465.6 $ 4,756.4 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. Three Months Ended September 30, 2019 Corporate Small Business Public Other Total Geography (1) United States $ 1,910.9 $ 386.2 $ 2,100.9 $ 7.6 $ 4,405.6 Rest of World 2.6 — — 499.5 502.1 Total Net sales 1,913.5 386.2 2,100.9 507.1 4,907.7 Major Product and Services Hardware 1,533.2 326.7 1,722.8 358.5 3,941.2 Software 263.6 47.4 313.2 65.7 689.9 Services 98.2 6.7 58.7 80.2 243.8 Other (2) 18.5 5.4 6.2 2.7 32.8 Total Net sales 1,913.5 386.2 2,100.9 507.1 4,907.7 Sales by Channel Corporate 1,913.5 — — — 1,913.5 Small Business — 386.2 — — 386.2 Government — — 793.4 — 793.4 Education — — 807.0 — 807.0 Healthcare — — 500.5 — 500.5 Other — — — 507.1 507.1 Total Net sales 1,913.5 386.2 2,100.9 507.1 4,907.7 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 1,743.4 364.0 1,939.3 443.8 4,490.5 Transferred at a point in time where CDW is agent 111.0 19.6 79.6 15.5 225.7 Transferred over time where CDW is principal 59.1 2.6 82.0 47.8 191.5 Total Net sales $ 1,913.5 $ 386.2 $ 2,100.9 $ 507.1 $ 4,907.7 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. Nine Months Ended September 30, 2020 Corporate Small Business Public Other Total Geography (1) United States $ 5,109.1 $ 1,030.6 $ 5,841.2 $ 16.1 $ 11,997.0 Rest of World 19.4 — — 1,494.9 1,514.3 Total Net sales 5,128.5 1,030.6 5,841.2 1,511.0 13,511.3 Major Product and Services Hardware 3,978.4 853.7 4,855.9 1,096.0 10,784.0 Software 799.2 139.5 764.3 238.8 1,941.8 Services 300.0 22.4 197.9 169.4 689.7 Other (2) 50.9 15.0 23.1 6.8 95.8 Total Net sales 5,128.5 1,030.6 5,841.2 1,511.0 13,511.3 Sales by Channel Corporate 5,128.5 — — — 5,128.5 Small Business — 1,030.6 — — 1,030.6 Government — — 2,135.9 — 2,135.9 Education — — 2,431.2 — 2,431.2 Healthcare — — 1,274.1 — 1,274.1 Other — — — 1,511.0 1,511.0 Total Net sales 5,128.5 1,030.6 5,841.2 1,511.0 13,511.3 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 4,602.4 961.3 5,339.1 1,332.9 12,235.7 Transferred at a point in time where CDW is agent 341.1 61.8 209.9 41.9 654.7 Transferred over time where CDW is principal 185.0 7.5 292.2 136.2 620.9 Total Net sales $ 5,128.5 $ 1,030.6 $ 5,841.2 $ 1,511.0 $ 13,511.3 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. Nine Months Ended September 30, 2019 Corporate Small Business Public Other Total Geography (1) United States $ 5,525.5 $ 1,119.2 $ 5,271.7 $ 24.8 $ 11,941.2 Rest of World 8.1 — — 1,546.2 1,554.3 Total Net sales 5,533.6 1,119.2 5,271.7 1,571.0 13,495.5 Major Product and Services Hardware 4,417.2 938.3 4,323.2 1,143.8 10,822.5 Software 777.4 144.2 783.1 212.4 1,917.1 Services 285.9 20.7 150.0 206.3 662.9 Other (2) 53.1 16.0 15.4 8.5 93.0 Total Net sales 5,533.6 1,119.2 5,271.7 1,571.0 13,495.5 Sales by Channel Corporate 5,533.6 — — — 5,533.6 Small Business — 1,119.2 — — 1,119.2 Government — — 1,860.2 — 1,860.2 Education — — 1,981.0 — 1,981.0 Healthcare — — 1,430.5 — 1,430.5 Other — — — 1,571.0 1,571.0 Total Net sales 5,533.6 1,119.2 5,271.7 1,571.0 13,495.5 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 5,033.4 1,054.7 4,908.0 1,383.7 12,379.8 Transferred at a point in time where CDW is agent 333.7 59.4 190.9 42.0 626.0 Transferred over time where CDW is principal 166.5 5.1 172.8 145.3 489.7 Total Net sales $ 5,533.6 $ 1,119.2 $ 5,271.7 $ 1,571.0 $ 13,495.5 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. The following table presents Net sales by major category for the three and nine months ended September 30, 2020 and 2019. Categories are based upon internal classifications. Three Months Ended September 30, 2020 2019 Net Sales Percentage Net Sales Percentage Notebooks/Mobile Devices $ 1,384.7 29.1 % $ 1,253.2 25.5 % Netcomm Products 525.8 11.1 566.7 11.5 Desktops 245.9 5.2 433.2 8.8 Video 315.9 6.6 353.4 7.2 Enterprise and Data Storage (Including Drives) 249.1 5.2 283.8 5.8 Other Hardware 1,070.8 22.5 1,050.9 21.4 Total Hardware 3,792.2 79.7 3,941.2 80.2 Software (1) 706.1 14.8 689.9 14.1 Services (1) 227.4 4.8 243.8 5.0 Other (2) 30.7 0.7 32.8 0.7 Total Net sales $ 4,756.4 100.0 % $ 4,907.7 100.0 % Nine Months Ended September 30, 2020 2019 Net Sales Percentage Net Sales Percentage Notebooks/Mobile Devices $ 3,923.1 29.0 % $ 3,334.2 24.7 % Netcomm Products 1,453.5 10.8 1,639.7 12.1 Desktops 882.5 6.5 1,148.6 8.5 Video 877.3 6.5 973.2 7.2 Enterprise and Data Storage (Including Drives) 690.0 5.1 850.8 6.3 Other Hardware 2,957.6 21.9 2,876.0 21.4 Total Hardware 10,784.0 79.8 10,822.5 80.2 Software (1) 1,941.8 14.4 1,917.1 14.2 Services (1) 689.7 5.1 662.9 4.9 Other (2) 95.8 0.7 93.0 0.7 Total Net sales $ 13,511.3 100.0 % $ 13,495.5 100.0 % (1) Certain software and services revenues are recorded on a net basis for accounting purposes. As a result, the category percentage of net revenues is not representative of the category percentage of gross profits. (2) Includes items such as delivery charges to customers.

Description of Business and S_2

Description of Business and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Description of Business	Description of Business CDW Corporation ("Parent"), a Fortune 500 company and member of the S&P 500 Index, is a market-leading provider of integrated information technology ("IT") solutions to small, medium and large business, government, education and healthcare customers in the United States ("US"), the United Kingdom ("UK") and Canada. The Company's offerings range from discrete hardware and software products to integrated IT solutions such as mobility, security, data center optimization, cloud computing, virtualization and collaboration. Throughout this report, the terms the "Company" and "CDW" refer to Parent and its 100% owned subsidiaries. Parent has two 100% owned subsidiaries, CDW LLC and CDW Finance Corporation. CDW LLC is an Illinois limited liability company that, together with its 100% owned subsidiaries, holds all material assets and conducts all business activities and operations of the Company. CDW Finance Corporation is a Delaware corporation formed for the sole purpose of acting as co-issuer of certain debt obligations and does not hold any material assets or engage in any business activities or operations.
Basis of Presentation	Basis of Presentation The accompanying unaudited interim Consolidated Financial Statements as of September 30, 2020 and for the three and nine months ended September 30, 2020 and 2019 (the "Consolidated Financial Statements") have been prepared in conformity with accounting principles generally accepted in the United States of America ("US GAAP") and the rules and regulations of the US Securities and Exchange Commission (the "SEC") for interim financial statements. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with US GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. These Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and the notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019 (the "December 31, 2019 Consolidated Financial Statements"). The significant accounting policies used in preparing these Consolidated Financial Statements were applied on a basis consistent with those reflected in the December 31, 2019 Consolidated Financial Statements. In the opinion of management, the Consolidated Financial Statements contain all adjustments (consisting of a normal, recurring nature) necessary to present fairly the Company's financial position, results of operations, comprehensive income, cash flows and changes in stockholders' equity as of the dates and for the periods indicated. The unaudited results of operations for such interim periods reported are not necessarily indicative of results for the full year.
Reclassification	Reclassifications Certain prior period amounts have been reclassified to conform with current period presentation.
Principles of Consolidation	Principles of Consolidation The Consolidated Financial Statements include the accounts of Parent and its 100% owned subsidiaries. All intercompany transactions and accounts are eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the Consolidated Financial Statements in accordance with US GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the Consolidated Financial Statements and the reported amounts of revenue and expenses during the reported periods. The Company bases its estimates on historical experience and on various other assumptions that management believes are reasonable under the circumstances including management’s current assumptions with respect to implications of the novel coronavirus (“COVID-19”) pandemic, the results of which form the basis for making judgments about carrying values of assets and liabilities that are not readily apparent from other sources. Actual results and outcomes could differ from those estimates.
Accounts Receivable	Accounts ReceivableThe Company estimates an allowance for credit losses related to accounts receivable for future expected credit losses by using relevant information such as historical information, current conditions, and reasonable and supportable forecasts. The allowance is measured on a pool basis when similar risk characteristics exist, and a loss-rate for each pool is determined using historical credit loss experience as the basis for the estimation of expected credit losses. Adjustments to historical loss information are made for differences in current conditions as well as changes in forecasted macroeconomic conditions, such as changes in the unemployment rate or gross domestic product growth rate.
Advertising	AdvertisingAdvertising costs are generally charged to expense in the period incurred and recorded in Selling and administrative expenses in the Consolidated Statements of Operations.
Recent Accounting Pronouncements	Reference Rate Reform In March 2020, the Financial Accounting Standards Board issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting. This ASU temporarily provides optional expedients and exceptions for applying existing guidance to contract modifications, hedging relationships and other transactions that are expected to be affected by reference rate reform. This ASU was effective upon its issuance and will remain in effect for all contract modifications and hedging relationships entered into through December 31, 2022. The adoption of this ASU along with the related expedients did not have an impact to the Company’s Consolidated Financial Statements. Measurement of Credit Losses on Financial Instruments On January 1, 2020, the Company adopted and applied Topic 326 using the modified retrospective approach. Topic 326 introduced a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables, which is reflected in the Company’s policies. The adoption of Topic 326, as well as the adjustment to retained earnings for the cumulative effect, was not significant to the Company's Consolidated Financial Statements.

Inventory Financing Agreements

Inventory Financing Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
Inventory Financing Agreements [Abstract]
Inventory Financing Agreements	Amounts included in Accounts payable-inventory financing are as follows: September 30, 2020 December 31, 2019 Revolving Loan inventory financing agreement (1) $ 608.9 $ 379.1 Other inventory financing agreements 52.3 50.8 Accounts payable-inventory financing $ 661.2 $ 429.9 (1) The senior secured asset-based revolving credit facility includes an inventory floorplan sub-facility that enables the Company to maintain an inventory financing agreement with a financial intermediary to facilitate the purchase of inventory from certain vendors on more favorable terms than offered directly by the vendors.

Contract Liabilities and Perf_2

Contract Liabilities and Performance Obligations (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction	The following table represents the total transaction price for the remaining performance obligations as of September 30, 2020 related to noncancelable contracts longer than 12 months in duration that is expected to be recognized over future periods. Within 1 Year Years 1-2 Years 2-3 Thereafter Remaining performance obligations $ 32.2 $ 20.6 $ 6.9 $ 0.3

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
Financial Instruments [Abstract]
Schedule of Cash Flow Hedges Included in AOCL	The following tables provide the activity in AOCL, net of tax, for the three and nine months ended September 30, 2020 and September 30, 2019. Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Change in fair value recorded to AOCL $ (0.4) $ (0.4) $ (0.6) $ (12.8) Reclassification from AOCL to Interest expense, net $ 1.6 $ 0.3 $ 4.1 $ 2.0

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	As of September 30, 2020 As of December 31, 2019 Maturity Date Interest Rate Amount Interest Rate Amount Credit Facilities CDW UK revolving credit facility (1) July 2021 — % $ — — % $ — Senior secured asset-based revolving credit facility March 2022 — % — 5.000 % 51.0 Total credit facilities — 51.0 Term Loans CDW UK term loan (1) August 2021 1.464 % 53.0 2.190 % 61.0 Senior secured term loan facility October 2026 1.900 % 1,427.1 3.550 % 1,438.3 Total term loans 1,480.1 1,499.3 Unsecured Senior Notes Senior notes due 2024 December 2024 5.500 % 575.0 5.500 % 575.0 Senior notes due 2025 May 2025 4.125 % 600.0 — % — Senior notes due 2025 September 2025 — % — 5.000 % 600.0 Senior notes due 2028 April 2028 4.250 % 600.0 4.250 % 600.0 Senior notes due 2029 February 2029 3.250 % 700.0 — % — Total unsecured senior notes 2,475.0 1,775.0 Other long-term obligations 4.4 12.6 Unamortized deferred financing fees (28.6) (20.6) Current maturities of long-term debt (72.3) (34.1) Total long-term debt $ 3,858.6 $ 3,283.2 (1) British pound-denominated debt facilities.
Carrying Value of Long-Term Debt	The approximate fair values and related carrying values of the Company's long-term debt, including current maturities and excluding unamortized discount and unamortized deferred financing fees, are as follows: September 30, 2020 December 31, 2019 Fair value $ 4,026.1 $ 3,447.5 Carrying value 3,959.5 3,337.9

Earnings per Share (Tables)

Earnings per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares	A reconciliation of basic weighted-average shares outstanding to diluted weighted-average shares outstanding is as follows: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Basic weighted-average shares outstanding 142.7 144.5 142.6 145.7 Effect of dilutive securities (1) 2.1 2.7 2.1 2.5 Diluted weighted-average shares outstanding (2) 144.8 147.2 144.7 148.2 (1) The dilutive effect of outstanding stock options, restricted stock units, restricted stock, performance share units and Coworker Stock Purchase Plan units is reflected in the diluted weighted-average shares outstanding using the treasury stock method. (2) There were fewer than 0.1 million potential common shares excluded from diluted weighted-average shares outstanding for both the three and nine months ended September 30, 2020 and 2019 as their inclusion would have had an anti-dilutive effect.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Information about the Company's segments is as follows: Corporate Small Business Public Other Headquarters Total Three Months Ended September 30, 2020 Net sales $ 1,660.0 $ 337.0 $ 2,293.8 $ 465.6 $ — $ 4,756.4 Operating income (loss) 128.5 24.3 196.1 18.7 (49.8) 317.8 Depreciation and amortization expense (22.4) (5.6) (77.2) (8.4) (18.8) (132.4) Three Months Ended September 30, 2019 Net sales $ 1,913.5 $ 386.2 $ 2,100.9 $ 507.1 $ — $ 4,907.7 Operating income (loss) 138.9 27.2 168.4 21.9 (35.8) 320.6 Depreciation and amortization expense (21.7) (5.6) (15.0) (7.9) (18.0) (68.2) Corporate Small Business Public Other Headquarters Total Nine Months Ended September 30, 2020 Net sales $ 5,128.5 $ 1,030.6 $ 5,841.2 $ 1,511.0 $ — $ 13,511.3 Operating income (loss) 378.9 72.6 468.4 49.9 (122.8) 847.0 Depreciation and amortization expense (66.8) (17.0) (184.0) (24.3) (56.9) (349.0) Nine Months Ended September 30, 2019 Net sales $ 5,533.6 $ 1,119.2 $ 5,271.7 $ 1,571.0 $ — $ 13,495.5 Operating income (loss) 430.8 78.2 373.9 66.6 (99.7) 849.8 Depreciation and amortization expense (64.8) (16.8) (41.4) (23.1) (51.4) (197.5)
Disaggregation of Revenue	Geographic Areas and Revenue Mix Three Months Ended September 30, 2020 Corporate Small Business Public Other Total Geography (1) United States $ 1,658.4 $ 337.0 $ 2,293.8 $ 6.1 $ 4,295.3 Rest of World 1.6 — — 459.5 461.1 Total Net sales 1,660.0 337.0 2,293.8 465.6 4,756.4 Major Product and Services Hardware 1,252.0 281.7 1,917.8 340.7 3,792.2 Software 284.9 43.3 304.7 73.2 706.1 Services 107.1 7.0 63.8 49.5 227.4 Other (2) 16.0 5.0 7.5 2.2 30.7 Total Net sales 1,660.0 337.0 2,293.8 465.6 4,756.4 Sales by Channel Corporate 1,660.0 — — — 1,660.0 Small Business — 337.0 — — 337.0 Government — — 847.7 — 847.7 Education — — 1,078.2 — 1,078.2 Healthcare — — 367.9 — 367.9 Other — — — 465.6 465.6 Total Net sales 1,660.0 337.0 2,293.8 465.6 4,756.4 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 1,474.2 313.9 2,080.3 407.7 4,276.1 Transferred at a point in time where CDW is agent 121.3 20.9 89.3 13.9 245.4 Transferred over time where CDW is principal 64.5 2.2 124.2 44.0 234.9 Total Net sales $ 1,660.0 $ 337.0 $ 2,293.8 $ 465.6 $ 4,756.4 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. Three Months Ended September 30, 2019 Corporate Small Business Public Other Total Geography (1) United States $ 1,910.9 $ 386.2 $ 2,100.9 $ 7.6 $ 4,405.6 Rest of World 2.6 — — 499.5 502.1 Total Net sales 1,913.5 386.2 2,100.9 507.1 4,907.7 Major Product and Services Hardware 1,533.2 326.7 1,722.8 358.5 3,941.2 Software 263.6 47.4 313.2 65.7 689.9 Services 98.2 6.7 58.7 80.2 243.8 Other (2) 18.5 5.4 6.2 2.7 32.8 Total Net sales 1,913.5 386.2 2,100.9 507.1 4,907.7 Sales by Channel Corporate 1,913.5 — — — 1,913.5 Small Business — 386.2 — — 386.2 Government — — 793.4 — 793.4 Education — — 807.0 — 807.0 Healthcare — — 500.5 — 500.5 Other — — — 507.1 507.1 Total Net sales 1,913.5 386.2 2,100.9 507.1 4,907.7 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 1,743.4 364.0 1,939.3 443.8 4,490.5 Transferred at a point in time where CDW is agent 111.0 19.6 79.6 15.5 225.7 Transferred over time where CDW is principal 59.1 2.6 82.0 47.8 191.5 Total Net sales $ 1,913.5 $ 386.2 $ 2,100.9 $ 507.1 $ 4,907.7 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. Nine Months Ended September 30, 2020 Corporate Small Business Public Other Total Geography (1) United States $ 5,109.1 $ 1,030.6 $ 5,841.2 $ 16.1 $ 11,997.0 Rest of World 19.4 — — 1,494.9 1,514.3 Total Net sales 5,128.5 1,030.6 5,841.2 1,511.0 13,511.3 Major Product and Services Hardware 3,978.4 853.7 4,855.9 1,096.0 10,784.0 Software 799.2 139.5 764.3 238.8 1,941.8 Services 300.0 22.4 197.9 169.4 689.7 Other (2) 50.9 15.0 23.1 6.8 95.8 Total Net sales 5,128.5 1,030.6 5,841.2 1,511.0 13,511.3 Sales by Channel Corporate 5,128.5 — — — 5,128.5 Small Business — 1,030.6 — — 1,030.6 Government — — 2,135.9 — 2,135.9 Education — — 2,431.2 — 2,431.2 Healthcare — — 1,274.1 — 1,274.1 Other — — — 1,511.0 1,511.0 Total Net sales 5,128.5 1,030.6 5,841.2 1,511.0 13,511.3 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 4,602.4 961.3 5,339.1 1,332.9 12,235.7 Transferred at a point in time where CDW is agent 341.1 61.8 209.9 41.9 654.7 Transferred over time where CDW is principal 185.0 7.5 292.2 136.2 620.9 Total Net sales $ 5,128.5 $ 1,030.6 $ 5,841.2 $ 1,511.0 $ 13,511.3 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. Nine Months Ended September 30, 2019 Corporate Small Business Public Other Total Geography (1) United States $ 5,525.5 $ 1,119.2 $ 5,271.7 $ 24.8 $ 11,941.2 Rest of World 8.1 — — 1,546.2 1,554.3 Total Net sales 5,533.6 1,119.2 5,271.7 1,571.0 13,495.5 Major Product and Services Hardware 4,417.2 938.3 4,323.2 1,143.8 10,822.5 Software 777.4 144.2 783.1 212.4 1,917.1 Services 285.9 20.7 150.0 206.3 662.9 Other (2) 53.1 16.0 15.4 8.5 93.0 Total Net sales 5,533.6 1,119.2 5,271.7 1,571.0 13,495.5 Sales by Channel Corporate 5,533.6 — — — 5,533.6 Small Business — 1,119.2 — — 1,119.2 Government — — 1,860.2 — 1,860.2 Education — — 1,981.0 — 1,981.0 Healthcare — — 1,430.5 — 1,430.5 Other — — — 1,571.0 1,571.0 Total Net sales 5,533.6 1,119.2 5,271.7 1,571.0 13,495.5 Timing of Revenue Recognition Transferred at a point in time where CDW is principal 5,033.4 1,054.7 4,908.0 1,383.7 12,379.8 Transferred at a point in time where CDW is agent 333.7 59.4 190.9 42.0 626.0 Transferred over time where CDW is principal 166.5 5.1 172.8 145.3 489.7 Total Net sales $ 5,533.6 $ 1,119.2 $ 5,271.7 $ 1,571.0 $ 13,495.5 (1) Net sales by geography is generally based on the ship-to address with the exception of certain services that may be performed at, or on behalf of, multiple locations. Such service arrangements are categorized based on the bill-to address. (2) Includes items such as delivery charges to customers. The following table presents Net sales by major category for the three and nine months ended September 30, 2020 and 2019. Categories are based upon internal classifications. Three Months Ended September 30, 2020 2019 Net Sales Percentage Net Sales Percentage Notebooks/Mobile Devices $ 1,384.7 29.1 % $ 1,253.2 25.5 % Netcomm Products 525.8 11.1 566.7 11.5 Desktops 245.9 5.2 433.2 8.8 Video 315.9 6.6 353.4 7.2 Enterprise and Data Storage (Including Drives) 249.1 5.2 283.8 5.8 Other Hardware 1,070.8 22.5 1,050.9 21.4 Total Hardware 3,792.2 79.7 3,941.2 80.2 Software (1) 706.1 14.8 689.9 14.1 Services (1) 227.4 4.8 243.8 5.0 Other (2) 30.7 0.7 32.8 0.7 Total Net sales $ 4,756.4 100.0 % $ 4,907.7 100.0 % Nine Months Ended September 30, 2020 2019 Net Sales Percentage Net Sales Percentage Notebooks/Mobile Devices $ 3,923.1 29.0 % $ 3,334.2 24.7 % Netcomm Products 1,453.5 10.8 1,639.7 12.1 Desktops 882.5 6.5 1,148.6 8.5 Video 877.3 6.5 973.2 7.2 Enterprise and Data Storage (Including Drives) 690.0 5.1 850.8 6.3 Other Hardware 2,957.6 21.9 2,876.0 21.4 Total Hardware 10,784.0 79.8 10,822.5 80.2 Software (1) 1,941.8 14.4 1,917.1 14.2 Services (1) 689.7 5.1 662.9 4.9 Other (2) 95.8 0.7 93.0 0.7 Total Net sales $ 13,511.3 100.0 % $ 13,495.5 100.0 % (1) Certain software and services revenues are recorded on a net basis for accounting purposes. As a result, the category percentage of net revenues is not representative of the category percentage of gross profits. (2) Includes items such as delivery charges to customers.

Description of Business and S_3

Description of Business and Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)subsidiary	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)subsidiary	Sep. 30, 2019USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of owned subsidiaries | subsidiary	2		2
Advertising costs	$ 47	$ 51	$ 140	$ 143
Provision for credit losses			30.4	$ 2.1
COVID- 19 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision for credit losses			$ 30

Inventory Financing Agreement_2

Inventory Financing Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Inventory Financing Agreements [Line Items]
Accounts payable-inventory financing	$ 661.2	$ 429.9
Accounts Payable, Inventory Financing
Inventory Financing Agreements [Line Items]
Revolving Loan inventory financing agreement	608.9	379.1
Other inventory financing agreements	$ 52.3	$ 50.8

Contract Liabilities and Perf_3

Contract Liabilities and Performance Obligations - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract liabilities	$ 247		$ 252
Revenue recognized from contract with customer	$ 157	$ 117

Contract Liabilities and Perf_4

Contract Liabilities and Performance Obligations - Schedule of Remaining Performance Obligations (Details) $ in Millions	Sep. 30, 2020USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 32.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 20.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 6.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 0.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, expected timing of satisfaction, period

Financial Instruments - (Detail

Financial Instruments - (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative [Line Items]
Interest rate cap, fair value	$ 1		$ 1		$ 1
Unrealized (loss) gain from hedge accounting	0.4	$ 0.4	0.6	$ 12.8
Interest Rate Cap
Derivative [Line Items]
Notional amount	2,800		2,800		2,800
Interest Rate Cap Agreement Maturity Date December 31, 2020
Derivative [Line Items]
Notional amount	1,400		1,400
Interest Rate Cap Agreement Maturity Date December 31, 2022
Derivative [Line Items]
Notional amount					$ 1,400
Interest Rate Contract
Derivative [Line Items]
Unrealized (loss) gain from hedge accounting	(0.4)	(0.4)	(0.6)	(12.8)
Amount expected to be reclassified from AOCL to interest expense in next twelve months			5
Derivative
Derivative [Line Items]
Interest income (expense) reclassified into earnings	$ 1.6	$ 0.3	$ 4.1	$ 2

Long-Term Debt - Debt Balances

Long-Term Debt - Debt Balances and Interest Rates (Details) - USD ($) $ in Millions	Sep. 30, 2020	Aug. 13, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt	$ 3,959.5		$ 3,337.9
Unamortized deferred financing fees	(28.6)		(20.6)
Current maturities of long-term debt	(72.3)		(34.1)
Total long-term debt	3,858.6		3,283.2
Total credit facilities
Debt Instrument [Line Items]
Long-term debt	$ 0		$ 51
CDW UK revolving credit facility
Debt Instrument [Line Items]
Interest rate in effect	0.00%		0.00%
Long-term debt	$ 0		$ 0
Senior secured asset-based revolving credit facility
Debt Instrument [Line Items]
Interest rate in effect	0.00%		5.00%
Long-term debt	$ 0		$ 51
Total term loans
Debt Instrument [Line Items]
Long-term debt	$ 1,480.1		$ 1,499.3
CDW UK term loan
Debt Instrument [Line Items]
Interest rate in effect	1.464%		2.19%
Long-term debt	$ 53		$ 61
Senior secured term loan facility
Debt Instrument [Line Items]
Interest rate in effect	1.90%		3.55%
Long-term debt	$ 1,427.1		$ 1,438.3
Total unsecured senior notes
Debt Instrument [Line Items]
Long-term debt	$ 2,475		$ 1,775
Senior notes due 2024
Debt Instrument [Line Items]
Interest rate in effect	5.50%		5.50%
Long-term debt	$ 575		$ 575
Senior notes due 2025
Debt Instrument [Line Items]
Interest rate in effect	4.125%		0.00%
Long-term debt	$ 600		$ 0
Senior notes due 2025
Debt Instrument [Line Items]
Interest rate in effect	0.00%
Long-term debt	$ 0	$ 600
Senior notes due 2028
Debt Instrument [Line Items]
Interest rate in effect	4.25%		4.25%
Long-term debt	$ 600		$ 600
Other long-term obligations
Debt Instrument [Line Items]
Long-term debt	$ 4.4		$ 12.6
Senior Notes due 2029
Debt Instrument [Line Items]
Interest rate in effect	3.25%		0.00%
Long-term debt	$ 700		$ 0

Long-Term Debt - Narrative (Det

Long-Term Debt - Narrative (Details)	Aug. 13, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2020GBP (£)	Sep. 30, 2020USD ($)	Apr. 21, 2020USD ($)	Dec. 31, 2019
CDW UK revolving credit facility
Debt Instrument [Line Items]
Borrowing capacity of the Revolving Loan			£ 50,000,000	$ 65,000,000
Interest rate in effect			0.00%	0.00%		0.00%
Senior secured asset-based revolving credit facility
Debt Instrument [Line Items]
Undrawn letters of credit				$ 1,000,000
Borrowing base				2,400,000,000
Additional borrowing capacity				$ 856,000,000
Interest rate in effect			0.00%	0.00%		5.00%
CDW UK term loan
Debt Instrument [Line Items]
Amount of restricted payment capacity under the loan			£ 173,000,000	$ 223,000,000
Interest rate in effect			1.464%	1.464%		2.19%
Senior secured term loan facility
Debt Instrument [Line Items]
Amount of restricted payment capacity under the loan				$ 2,100,000,000
Periodic payment, principal		$ 4,000,000
Interest rate in effect			1.90%	1.90%		3.55%
Senior notes due 2025
Debt Instrument [Line Items]
Interest rate in effect			0.00%	0.00%
Interest rate, stated percentage	5.00%
Percentage of principal amount redeemed	103.75%
Accounts Payable, Inventory Financing | Senior secured asset-based revolving credit facility
Debt Instrument [Line Items]
Amount owed under Revolving loan financing agreement				$ 594,000,000
Senior notes due 2025 | Unsecured senior debt
Debt Instrument [Line Items]
Debt instrument, aggregate principal amount					$ 600,000,000
Interest rate, stated percentage					4.125%
Senior Notes due 2029 | Unsecured senior debt
Debt Instrument [Line Items]
Debt instrument, aggregate principal amount	$ 700,000,000
Interest rate, stated percentage	3.25%

Long-Term Debt - Fair Value of

Long-Term Debt - Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value	$ 3,959.5	$ 3,337.9
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	$ 4,026.1	$ 3,447.5

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax (expense) benefit	$ (56.9)	$ (59.2)	$ (157.1)	$ (162.5)
Effective income tax rate reconciliation, percent	22.70%		22.20%	22.80%

Earnings per Share (Details)

Earnings per Share (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Basic weighted-average shares outstanding (in shares)	142.7	144.5	142.6	145.7
Effect of dilutive securities (in shares)	2.1	2.7	2.1	2.5
Diluted weighted-average shares outstanding (in shares)	144.8	147.2	144.7	148.2
Anti-dilutive shares (fewer than) (in shares)	0.1	0.1	0.1	0.1

Segment Information - Narrative

Segment Information - Narrative (Details)	9 Months Ended
	Sep. 30, 2020segmentemployee
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
Number of operating segments which do not meet reportable unit quantitative threshold | segment	2
Minimum | Corporate
Segment Reporting Information [Line Items]
Customer segments, customer employee headcount | employee	250
Maximum | Small Business
Segment Reporting Information [Line Items]
Customer segments, customer employee headcount | employee	250

Segment Information - Schedule

Segment Information - Schedule of Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net sales	$ 4,756.4	$ 4,907.7	$ 13,511.3	$ 13,495.5
Income (loss) from operations	317.8	320.6	847	849.8
Depreciation and amortization expense	(132.4)	(68.2)	(349)	(197.5)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	1,660	1,913.5	5,128.5	5,533.6
Income (loss) from operations	128.5	138.9	378.9	430.8
Depreciation and amortization expense	(22.4)	(21.7)	(66.8)	(64.8)
Operating Segments | Small Business
Segment Reporting Information [Line Items]
Net sales	337	386.2	1,030.6	1,119.2
Income (loss) from operations	24.3	27.2	72.6	78.2
Depreciation and amortization expense	(5.6)	(5.6)	(17)	(16.8)
Operating Segments | Public
Segment Reporting Information [Line Items]
Net sales	2,293.8	2,100.9	5,841.2	5,271.7
Income (loss) from operations	196.1	168.4	468.4	373.9
Depreciation and amortization expense	(77.2)	(15)	(184)	(41.4)
Operating Segments | Other
Segment Reporting Information [Line Items]
Net sales	465.6	507.1	1,511	1,571
Income (loss) from operations	18.7	21.9	49.9	66.6
Depreciation and amortization expense	(8.4)	(7.9)	(24.3)	(23.1)
Headquarters
Segment Reporting Information [Line Items]
Net sales	0	0	0	0
Income (loss) from operations	(49.8)	(35.8)	(122.8)	(99.7)
Depreciation and amortization expense	$ (18.8)	$ (18)	$ (56.9)	$ (51.4)

Segment Information - Disaggreg

Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Net sales	$ 4,756.4	$ 4,907.7	$ 13,511.3	$ 13,495.5
Percentage of Total Net Sales	100.00%	100.00%	100.00%	100.00%
Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 1,660	$ 1,913.5	$ 5,128.5	$ 5,533.6
Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	337	386.2	1,030.6	1,119.2
Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	2,293.8	2,100.9	5,841.2	5,271.7
Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	465.6	507.1	1,511	1,571
Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	4,276.1	4,490.5	12,235.7	12,379.8
Transferred at a point in time where CDW is principal | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,474.2	1,743.4	4,602.4	5,033.4
Transferred at a point in time where CDW is principal | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	313.9	364	961.3	1,054.7
Transferred at a point in time where CDW is principal | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	2,080.3	1,939.3	5,339.1	4,908
Transferred at a point in time where CDW is principal | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	407.7	443.8	1,332.9	1,383.7
Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Net sales	245.4	225.7	654.7	626
Transferred at a point in time where CDW is agent | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	121.3	111	341.1	333.7
Transferred at a point in time where CDW is agent | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	20.9	19.6	61.8	59.4
Transferred at a point in time where CDW is agent | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	89.3	79.6	209.9	190.9
Transferred at a point in time where CDW is agent | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	13.9	15.5	41.9	42
Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	234.9	191.5	620.9	489.7
Transferred over time where CDW is principal | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	64.5	59.1	185	166.5
Transferred over time where CDW is principal | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	2.2	2.6	7.5	5.1
Transferred over time where CDW is principal | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	124.2	82	292.2	172.8
Transferred over time where CDW is principal | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	44	47.8	136.2	145.3
Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,660	1,913.5	5,128.5	5,533.6
Corporate | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,660	1,913.5	5,128.5	5,533.6
Corporate | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Corporate | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Corporate | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Small Business
Disaggregation of Revenue [Line Items]
Net sales	337	386.2	1,030.6	1,119.2
Small Business | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Small Business | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	337	386.2	1,030.6	1,119.2
Small Business | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Small Business | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Government
Disaggregation of Revenue [Line Items]
Net sales	847.7	793.4	2,135.9	1,860.2
Government | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Government | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Government | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	847.7	793.4	2,135.9	1,860.2
Government | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Education
Disaggregation of Revenue [Line Items]
Net sales	1,078.2	807	2,431.2	1,981
Education | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Education | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Education | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	1,078.2	807	2,431.2	1,981
Education | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Healthcare
Disaggregation of Revenue [Line Items]
Net sales	367.9	500.5	1,274.1	1,430.5
Healthcare | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Healthcare | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Healthcare | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	367.9	500.5	1,274.1	1,430.5
Healthcare | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Net sales	465.6	507.1	1,511	1,571
Other | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Other | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Other | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Other | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	465.6	507.1	1,511	1,571
Hardware
Disaggregation of Revenue [Line Items]
Net sales	$ 3,792.2	$ 3,941.2	$ 10,784	$ 10,822.5
Percentage of Total Net Sales	79.70%	80.20%	79.80%	80.20%
Hardware | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 1,252	$ 1,533.2	$ 3,978.4	$ 4,417.2
Hardware | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	281.7	326.7	853.7	938.3
Hardware | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	1,917.8	1,722.8	4,855.9	4,323.2
Hardware | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	340.7	358.5	1,096	1,143.8
Notebooks/Mobile Devices
Disaggregation of Revenue [Line Items]
Net sales	$ 1,384.7	$ 1,253.2	$ 3,923.1	$ 3,334.2
Percentage of Total Net Sales	29.10%	25.50%	29.00%	24.70%
Netcomm Products
Disaggregation of Revenue [Line Items]
Net sales	$ 525.8	$ 566.7	$ 1,453.5	$ 1,639.7
Percentage of Total Net Sales	11.10%	11.50%	10.80%	12.10%
Desktops
Disaggregation of Revenue [Line Items]
Net sales	$ 245.9	$ 433.2	$ 882.5	$ 1,148.6
Percentage of Total Net Sales	5.20%	8.80%	6.50%	8.50%
Video
Disaggregation of Revenue [Line Items]
Net sales	$ 315.9	$ 353.4	$ 877.3	$ 973.2
Percentage of Total Net Sales	6.60%	7.20%	6.50%	7.20%
Enterprise and Data Storage (Including Drives)
Disaggregation of Revenue [Line Items]
Net sales	$ 249.1	$ 283.8	$ 690	$ 850.8
Percentage of Total Net Sales	5.20%	5.80%	5.10%	6.30%
Other Hardware
Disaggregation of Revenue [Line Items]
Net sales	$ 1,070.8	$ 1,050.9	$ 2,957.6	$ 2,876
Percentage of Total Net Sales	22.50%	21.40%	21.90%	21.40%
Software
Disaggregation of Revenue [Line Items]
Net sales	$ 706.1	$ 689.9	$ 1,941.8	$ 1,917.1
Percentage of Total Net Sales	14.80%	14.10%	14.40%	14.20%
Software | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 284.9	$ 263.6	$ 799.2	$ 777.4
Software | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	43.3	47.4	139.5	144.2
Software | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	304.7	313.2	764.3	783.1
Software | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	73.2	65.7	238.8	212.4
Services
Disaggregation of Revenue [Line Items]
Net sales	$ 227.4	$ 243.8	$ 689.7	$ 662.9
Percentage of Total Net Sales	4.80%	5.00%	5.10%	4.90%
Services | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 107.1	$ 98.2	$ 300	$ 285.9
Services | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	7	6.7	22.4	20.7
Services | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	63.8	58.7	197.9	150
Services | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	49.5	80.2	169.4	206.3
Other
Disaggregation of Revenue [Line Items]
Net sales	$ 30.7	$ 32.8	$ 95.8	$ 93
Percentage of Total Net Sales	0.70%	0.70%	0.70%	0.70%
Other | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 16	$ 18.5	$ 50.9	$ 53.1
Other | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	5	5.4	15	16
Other | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	7.5	6.2	23.1	15.4
Other | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	2.2	2.7	6.8	8.5
United States
Disaggregation of Revenue [Line Items]
Net sales	4,295.3	4,405.6	11,997	11,941.2
United States | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	1,658.4	1,910.9	5,109.1	5,525.5
United States | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	337	386.2	1,030.6	1,119.2
United States | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	2,293.8	2,100.9	5,841.2	5,271.7
United States | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	6.1	7.6	16.1	24.8
Rest of World
Disaggregation of Revenue [Line Items]
Net sales	461.1	502.1	1,514.3	1,554.3
Rest of World | Operating Segments | Corporate
Disaggregation of Revenue [Line Items]
Net sales	1.6	2.6	19.4	8.1
Rest of World | Operating Segments | Small Business
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Rest of World | Operating Segments | Public
Disaggregation of Revenue [Line Items]
Net sales	0	0	0	0
Rest of World | Operating Segments | Other
Disaggregation of Revenue [Line Items]
Net sales	$ 459.5	$ 499.5	$ 1,494.9	$ 1,546.2