CDW (CDW) 10-K 1 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	CDW Corp
Entity Central Index Key	1,402,057
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 9,577.6
Entity Common Stock, Shares Outstanding		152,423,423

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 144.2	$ 263.7
Accounts receivable, net of allowance for doubtful accounts of $6.2 and $5.9, respectively	2,320.5	2,168.6
Merchandise inventory	449.5	452
Miscellaneous receivables	336.5	234.9
Prepaid expenses and other	127.4	118.9
Total current assets	3,378.1	3,238.1
Property and equipment, net	161.1	163.7
Goodwill	2,479.6	2,455
Other intangible assets, net	897	1,055.6
Other assets	40.8	36
Total Assets	6,956.6	6,948.4
Current liabilities:
Accounts payable-trade	1,317.7	1,072.9
Accounts payable-inventory financing	498	580.4
Current maturities of long-term debt	25.5	18.5
Deferred revenue	194	172.6
Accrued expenses and other current liabilities:
Compensation	129.5	167.6
Interest	21.6	25.1
Sales taxes	43.8	38
Advertising	89.2	55.8
Income taxes	15.1	2.6
Other	180.2	147.2
Total current liabilities	2,514.6	2,280.7
Long-term liabilities:
Debt	3,210	3,215.9
Deferred income taxes	196.3	369.2
Other liabilities	52.8	37.1
Total long-term liabilities	3,459.1	3,622.2
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, 1,000.0 shares authorized; 153.1 and 160.3 shares issued, respectively	1.5	1.6
Less: treasury stock, $0.01 par value, 0.1 and 0 shares held, respectively	0	0
Outstanding common stock, $0.01 par value, 153.0 and 160.3 shares outstanding, respectively	1.5	1.6
Paid-in capital	2,911.6	2,857.3
Accumulated deficit	(1,834.3)	(1,673.8)
Accumulated other comprehensive loss	(95.9)	(139.6)
Total stockholders’ equity	982.9	1,045.5
Total Liabilities and Stockholders’ Equity	$ 6,956.6	$ 6,948.4

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6.2	$ 5.9
Preferred shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred shares, authorized (in shares)	100	100
Preferred shares, issued (in shares)	0	0
Preferred shares, outstanding (in shares)	0	0
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, authorized (in shares)	1,000	1,000
Common shares, issued (in shares)	153.1	160.3
Common shares, outstanding (in shares)	153	160.3
Treasury shares, par value (in dollars per share)	$ 0.01
Treasury stock, shares held (in shares)	0.1	0

Consolidated Statements Of Oper

Consolidated Statements Of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Cost of sales									12,741.6	11,654.7	10,872.9
Gross profit	614.4	642	641.1	552.6	577.9	614.3	610.5	524.5	2,449.9	2,327.2	2,115.8
Selling and administrative expenses									1,410.1	1,345.1	1,226
Advertising expense									173.7	162.9	147.8
Income from operations	221.6	243.7	231.1	169.8	197.2	237.5	223.5	161	866.1	819.2	742
Interest expense, net									(150.5)	(146.5)	(159.5)
Net loss on extinguishments of long-term debt									(57.4)	(2.1)	(24.3)
Gain on remeasurement of equity investment									0	0	98.1
Other income (expense), net									2.1	1.8	(9.3)
Income before income taxes									660.3	672.4	647
Income tax expense									(137.3)	(248)	(243.9)
Net income	$ 195.2	$ 129.2	$ 141	$ 57.6	$ 103.2	$ 125.9	$ 117.5	$ 77.8	$ 523	$ 424.4	$ 403.1
Net income per common share:
Earnings per share, basic (in dollars per share)	$ 1.28	$ 0.84	$ 0.90	$ 0.36	$ 0.64	$ 0.78	$ 0.71	$ 0.47	$ 3.37	$ 2.59	$ 2.37
Earnings per share, diluted (in dollars per share)	1.26	0.83	0.89	0.35	0.63	0.76	0.70	0.46	$ 3.31	$ 2.56	$ 2.35
Weighted Average Number of Shares Outstanding, Basic [Abstract]
Basic weighted-average shares outstanding (in shares)									155.4	163.6	170.3
Diluted weighted-average shares outstanding (in shares)									158.2	166	171.8
Cash dividends declared per common share (in dollars per share)	$ 0.2100	$ 0.1600	$ 0.1600	$ 0.1600	$ 0.1600	$ 0.1075	$ 0.1075	$ 0.1075	$ 0.6900	$ 0.4825	$ 0.3100

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income		$ 523		$ 424.4	$ 403.1
Foreign currency translation, net	[1]	43.5		(78.5)	(44.5)
Unrealized gain from hedge accounting, net		0.2	[2]	0	0
Other comprehensive income (loss), net of tax		43.7		(78.5)	(44.5)
Comprehensive income		566.7		345.9	358.6
Tax expense (benefit) on foreign currency translation		0.2		$ 0.2	$ 0.3
Tax expense (benefit) on unrealized loss from hedge accounting		$ 0.1
[1]	Net of tax expense of $0.2 million, $0.2 million and $0.3 million, respectively.
[2]	Net of tax expense of $0.1 million for 2017.

Consolidated Statement Of Share

Consolidated Statement Of Shareholders' Equity - USD ($) $ in Millions	Total		Preferred Stock	Common Stock	Treasury Stock	Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2014			0	172,200,000	0
Beginning balance at Dec. 31, 2014	$ 936.5		$ 0	$ 1.7	$ 0	$ 2,711.9	$ (1,760.5)	$ (16.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-based compensation expense	28.3					28.3
Stock option exercises (in shares)				100,000
Stock option exercises	2.4					2.4
Common stock issued for equity-based compensation (in shares)				300,000
Common stock issued for equity-based compensation	0					0
Excess tax benefits from equity-based compensation	0.6					0.6
Coworker Stock Purchase Plan (in shares)				300,000
Coworker Stock Purchase Plan	8.7					8.7
Common stock issued for acquisition of business (in shares)				1,600,000
Common stock issued for acquisition of business	55					55
Dividends paid	(52.9)						(52.9)
Net income	403.1						403.1
Repurchases of common stock (in shares)				(6,300,000)
Repurchases of common stock	(241.3)						(241.3)
Foreign currency translation	(44.5)	[1]						(44.5)
Ending balance (in shares) at Dec. 31, 2015			0	168,200,000	0
Ending balance at Dec. 31, 2015	1,095.9		$ 0	$ 1.7	$ 0	2,806.9	(1,651.6)	(61.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-based compensation expense	33.2					33.2
Stock option exercises (in shares)				400,000
Stock option exercises	7.4					7.4
Common stock issued for equity-based compensation (in shares)				200,000
Common stock issued for equity-based compensation	0
Coworker Stock Purchase Plan (in shares)				200,000
Coworker Stock Purchase Plan	9.3					9.3
Dividends paid	(78.7)					0.5	(79.2)
Net income	424.4						424.4
Repurchases of common stock (in shares)				(8,700,000)
Repurchases of common stock	(367.5)			$ (0.1)			(367.4)
Foreign currency translation	(78.5)	[1]						(78.5)
Ending balance (in shares) at Dec. 31, 2016			0	160,300,000	0
Ending balance at Dec. 31, 2016	1,045.5		$ 0	$ 1.6	$ 0	2,857.3	(1,673.8)	(139.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-based compensation expense	$ 37.9					37.9
Stock option exercises (in shares)	476,520			1,500,000
Stock option exercises	$ 13					13
Coworker Stock Purchase Plan (in shares)				200,000
Coworker Stock Purchase Plan	10.3					10.3
Dividends paid	(106.9)					0.7	(107.6)
Incentive compensation plan shares withheld for taxes (in shares)					100,000
Incentive compensation plan shares withheld for taxes	(49.6)					(7.6)	(42)
Net income	523						523
Repurchases of common stock (in shares)				(8,900,000)
Repurchases of common stock	(534)			$ (0.1)			(533.9)
Unrealized gain from hedge accounting	0.2							0.2
Foreign currency translation	43.5	[1]						43.5
Ending balance (in shares) at Dec. 31, 2017			0	153,100,000	100,000
Ending balance at Dec. 31, 2017	$ 982.9		$ 0	$ 1.5	$ 0	$ 2,911.6	$ (1,834.3)	$ (95.9)
[1]	Net of tax expense of $0.2 million, $0.2 million and $0.3 million, respectively.

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Cash Flows [Abstract]
Net income	$ 523	$ 424.4	$ 403.1
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	260.9	254.5	227.4
Equity-based compensation expense	43.7	39.2	31.2
Deferred income taxes	(172.7)	(97.2)	(54.5)
Amortization of deferred financing costs, debt premium and debt discount, net	5.2	6.5	6.4
Net loss on extinguishments of long-term debt	57.4	2.1	24.3
Loss from equity investments	0	0	11.2
Gain on remeasurement of equity investment	0	0	(98.1)
Mark-to-market (gain) loss on interest rate cap agreements	(0.5)	(2.6)	2.1
Other	0.4	0.4	0.3
Changes in assets and liabilities:
Accounts receivable	(128.4)	(179.9)	(342.6)
Merchandise inventory	8.5	(68.5)	(31.5)
Other assets	(116.4)	(50.1)	(71.2)
Accounts payable-trade	231.5	225.1	100.5
Other current liabilities	51.4	80.2	47.5
Long-term liabilities	13.7	(30.1)	21.4
Net cash provided by operating activities	777.7	604	277.5
Cash flows used in investing activities:
Capital expenditures	(81.1)	(63.5)	(90.1)
Premium payments on interest rate cap agreements	0	(2.4)	(0.5)
Acquisition of business, net of cash acquired	0	0	(263.8)
Net cash used in investing activities	(81.1)	(65.9)	(354.4)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	1,560.7	338.8	314.5
Repayments of borrowings under revolving credit facility	(1,560.7)	(338.8)	(314.5)
Repayments of long-term debt	(14.9)	(20.6)	(32.8)
Proceeds from issuance of long-term debt	2,083	1,483	525
Payments to extinguish long-term debt	(2,121.3)	(1,490.4)	(525.3)
Net change in other long-term obligation	(3.8)	15.7	0
Payments of debt financing costs	(9.6)	(5.9)	(6.8)
Net change in accounts payable-inventory financing	(84)	143.6	95.9
Effective portion of interest rate cap agreements	0.4	0	0
Proceeds from stock option exercises	13	7.4	2.4
Proceeds from Coworker Stock Purchase Plan	10.3	9.3	8.7
Repurchases of common stock	(534)	(367.4)	(241.3)
Payment of incentive compensation plan withholding taxes	(49.6)	0	(0.6)
Dividends	(106.9)	(78.7)	(52.9)
Principal payments under capital lease obligations	(1.3)	(0.6)	0
Net cash (used in) provided by financing activities	(818.7)	(304.6)	(226.5)
Effect of exchange rate changes on cash and cash equivalents	2.6	(7.4)	(3.5)
Net (decrease) increase in cash and cash equivalents	(119.5)	226.1	(306.9)
Cash and cash equivalents – beginning of period	263.7	37.6	344.5
Cash and cash equivalents – end of period	144.2	263.7	37.6
Supplementary disclosure of cash flow information:
Interest paid	(148.5)	(144.3)	(154.6)
Taxes paid, net	$ (275.7)	$ (329.2)	$ (300.2)

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
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”) is a Fortune 500 company with multi-national capabilities and a 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 as described in Note 19 (Supplemental Guarantor Information) and does not hold any material assets or engage in any business activities or operations. In August 2015, the Company completed the acquisition of Kelway TopCo Limited (“Kelway”), a UK-based IT solutions provider with global offerings by purchasing the remaining 65% of its outstanding common stock, which increased the Company’s ownership interest from 35% to 100% and provided the Company control. In 2016 Kelway was rebranded CDW UK. Basis of Presentation The Consolidated Financial Statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and the rules and regulations of the US Securities and Exchange Commission (“SEC”). 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 GAAP requires management to make use of 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, 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 could differ from those estimates. Business Combinations The Company accounts for all business combinations using the acquisition method of accounting, which allocates the fair value of the purchase consideration to the tangible and intangible assets acquired and liabilities assumed based on their estimated fair values. The excess of the purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. When determining the fair values of assets acquired and liabilities assumed, management makes significant estimates and assumptions. The Company may utilize third-party valuation specialists to assist the Company in the allocation. Initial purchase price allocations are subject to revision within the measurement period, not to exceed one year from the date of acquisition. Acquisition-related expenses and transaction costs associated with business combinations are expensed as incurred. Cash and Cash Equivalents Cash and cash equivalents include all deposits in banks and short-term (original maturities of three months or less at the time of purchase), highly liquid investments that are readily convertible to known amounts of cash and are so near maturity that there is insignificant risk of changes in value due to interest rate changes. Accounts Receivable Trade accounts receivable are recorded at the invoiced amount and typically do not bear interest. The Company provides allowances for doubtful accounts related to accounts receivable for estimated losses resulting from the inability of its customers to make required payments. The Company takes into consideration the overall quality of the receivable portfolio along with specifically-identified customer risks in establishing the allowance. Merchandise Inventory Inventory is valued at the lower of cost and net realizable value. Cost is determined using a weighted-average cost method. Price protection is recorded when earned as a reduction to the cost of inventory. The Company decreases the value of inventory for estimated obsolescence equal to the difference between the cost of inventory and the net realizable value, based upon an aging analysis of the inventory on hand, specifically known inventory-related risks, and assumptions about future demand and market conditions. Miscellaneous Receivables Miscellaneous receivables primarily consist of amounts due from vendors. The Company receives incentives from vendors related to cooperative advertising, volume rebates, bid programs, price protection and other programs. These incentives generally relate to written vendor agreements with specified performance requirements and are recorded as adjustments to Cost of sales or Merchandise inventory, depending on the nature of the incentive. Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. The Company calculates depreciation expense using the straight-line method over the estimated useful lives of the assets. Property and equipment are reviewed annually to determine whether there is any impairment. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. If the carrying amount of an asset exceeds its estimated future undiscounted cash flows, an impairment loss is recorded for the excess of the asset’s carrying amount over its fair value. Leasehold improvements are amortized over the shorter of their estimated useful lives or the initial lease term. Expenditures for major renewals and improvements that extend the useful life of property and equipment are capitalized. Expenditures for maintenance and repairs are charged to expense as incurred. The estimated useful lives of property and equipment are as follows: Classification Estimated Machinery and equipment 5 to 10 years Building and leasehold improvements 5 to 25 years Computer and data processing equipment 3 to 5 years Computer software 3 to 5 years Furniture and fixtures 5 to 10 years The Company has asset retirement obligations associated with commitments to return property subject to the terms of operating leases to its original condition upon lease termination. At December 31, 2017 and 2016 , the Company’s asset retirement liability was less than $2 million and $1 million , respectively. Equity Investments If the Company is not required to consolidate its investment in another entity because it does not have control, the Company uses the equity method if it (i) can exercise significant influence over the other entity and (ii) holds common stock of the other entity. Under the equity method, investments are carried at cost, plus or minus the Company’s share of equity in the increases and decreases in the investee’s net assets after the date of acquisition and adjustments for basis differences. The Company’s share of the income or loss of equity method investees is included in Other income (expense), net in the Consolidated Statements of Operations. Goodwill The Company performs an evaluation of goodwill, utilizing either a qualitative or quantitative impairment test. A qualitative assessment is performed at least on an annual basis to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying value. The Company performs a quantitative impairment test for each reporting unit every three years, or more frequently if circumstances indicate a potential impairment. The annual test for impairment is conducted as of December 1. The Company’s reporting units included in the assessment of potential goodwill impairment are the same as its operating segments. Goodwill is not amortized but is subject to periodic testing for impairment at the reporting unit level. Under a qualitative assessment, the most recent quantitative assessment is used to determine if it is more- likely-than-not that the reporting unit’s goodwill is impaired. As part of this qualitative assessment, the Company assesses relevant events and circumstances including macroeconomic conditions, industry and market conditions, cost factors, overall financial performance, changes in share price and entity-specific events to determine if there is an indication of impairment. Under a quantitative assessment, goodwill impairment is identified by comparing the fair value of a reporting unit to its carrying amount, including goodwill. If the carrying amount of a reporting unit exceeds its fair value, goodwill is considered impaired and an impairment charge is recognized in an amount equal to that excess, not to exceed the carrying amount of goodwill. Fair value of a reporting unit is determined by using a weighted combination of an income approach ( 75% ) and a market approach ( 25% ), as this combination is considered the most indicative of the Company’s fair value in an orderly transaction between market participants. Under the income approach, the Company determines fair value based on estimated future cash flows of a reporting unit, discounted by an estimated weighted-average cost of capital, which reflects the overall level of inherent risk of a reporting unit and the rate of return an outside investor would expect to earn. The estimated future cash flows of each reporting unit are based on internally generated forecasts for the remainder of the respective reporting period and the next five years . The Company uses a range of 2.0 - 3.5% long-term assumed consolidated annual Net sales growth rate for periods after the terminal year. Under the market approach, the Company utilizes valuation multiples derived from publicly available information for guideline companies to provide an indication of how much a knowledgeable investor in the marketplace would be willing to pay for a company. The valuation multiples are applied to the reporting units. Determining the fair value of a reporting unit is judgmental in nature and requires the use of significant estimates and assumptions, including Net sales growth rates, gross profit margins, operating margins, discount rates and future market conditions, among others. Any changes in the judgments, estimates or assumptions used could produce significantly different results. Intangible Assets Intangible assets with determinable lives are amortized on a straight-line basis over their respective estimated useful lives. The cost of computer software developed or obtained for internal use is capitalized and amortized on a straight-line basis over the estimated useful life of the software. Intangible assets are reviewed for impairment when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. If the carrying amount of an asset exceeds its estimated future undiscounted cash flows, an impairment loss is recorded for the excess of the asset’s carrying amount over its fair value. In addition, each quarter, the Company evaluates whether events and circumstances warrant a revision to the remaining estimated useful life of each of these intangible assets. If the Company were to determine that a change to the remaining estimated useful life of an intangible asset was necessary, then the remaining carrying amount of the intangible asset would be amortized prospectively over that revised remaining useful life. The following table shows estimated useful lives of definite-lived intangible assets: Classification Estimated Customer relationships and contracts 3 to 14 years Trade name generally 20 years Internally developed software 3 to 5 years Other 1 to 10 years Deferred Financing Costs Deferred financing costs, such as underwriting, financial advisory, professional fees and other similar fees are capitalized and recognized in Interest expense, net over the estimated life of the related debt instrument using the effective interest method or straight-line method, as applicable. The Company classifies deferred financing costs as a direct deduction from the carrying value of the Long-term debt liability on the Consolidated Balance Sheets, except for deferred financing costs associated with revolving credit facilities which are presented as an asset, within Other assets on the Consolidated Balance Sheets. Derivative Instruments The Company has interest rate cap agreements for the purpose of hedging its exposure to fluctuations in interest rates. The interest rate cap agreements are designated as cash flow hedges of interest rate risk and recorded at fair value in Other assets on the Consolidated Balance Sheets. The gain or loss on the derivative instruments is reported as a component of Accumulated other comprehensive loss until reclassified to Interest expense in the same period the hedge transaction affects earnings. Fair Value Measurements Fair value is defined under GAAP as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A fair value hierarchy has been established for valuation inputs to prioritize the inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market. Each fair value measurement is reported in one of the three levels which is determined by the lowest level input that is significant to the fair value measurement in its entirety. These levels are: Level 1 – observable inputs such as quoted prices for identical instruments traded in active markets. Level 2 – inputs are based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 – inputs are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability. The fair values are therefore determined using model-based techniques that include option pricing models, discounted cash flow models and similar techniques. Accumulated Other Comprehensive Loss The components of Accumulated other comprehensive loss included in Stockholders’ equity are as follows: Years Ended December 31, (in millions) 2017 2016 2015 Foreign currency translation $ (96.1 ) $ (139.6 ) $ (61.1 ) Unrealized gain from hedge accounting 0.2 — — Accumulated other comprehensive loss $ (95.9 ) $ (139.6 ) $ (61.1 ) Revenue Recognition The Company is a primary distribution channel for a large group of vendors and suppliers, including original equipment manufacturers (“OEMs”), software publishers, wholesale distributors and cloud providers. The Company records revenue from sales transactions when title and risk of loss are passed to the customer, there is persuasive evidence of an arrangement for sale, delivery has occurred and/or services have been rendered, the sales price is fixed or determinable, and collectability is reasonably assured. The Company’s shipping terms typically specify F.O.B. destination, at which time title and risk of loss have passed to the customer. Revenues from the sales of hardware products and software licenses are generally recognized on a gross basis with the selling price to the customer recorded as sales and the acquisition cost of the product recorded as cost of sales. These items can be delivered to customers in a variety of ways, including (i) as physical product shipped from the Company’s warehouse, (ii) via drop-shipment by the vendor or supplier, or (iii) via electronic delivery for software licenses. At the time of sale, the Company records an estimate for sales returns and allowances based on historical experience. The Company’s vendor partners warrant most of the products the Company sells. The Company leverages drop-shipment arrangements with many of its vendors and suppliers to deliver products to its customers without having to physically hold the inventory at its warehouses, thereby increasing efficiency and reducing costs. The Company recognizes revenue for drop-shipment arrangements on a gross basis upon delivery to the customer with contract terms that typically specify F.O.B. destination. Revenue from professional services is either recognized as provided for services billed at an hourly rate, recognized using a percentage of completion model for fixed fee project work or recognized using a proportional performance model for services provided at a fixed fee. Revenues for cloud computing solutions including Software as a Service (“SaaS”) and Infrastructure as a Service (“IaaS”) arrangements with one time invoicing to the customer are recognized at the time of invoice. Revenues for data center services such as managed and remote managed services, server co-location, internet connectivity, data backup and storage, and SaaS and IaaS arrangements where the customer is invoiced over time are recognized over the period service is provided. The Company also sells certain products for which it acts as an agent. Products in this category include the sale of third-party services, warranties, software assurance (“SA”) and third-party hosted SaaS and IaaS arrangements. SA is a product that allows customers to upgrade, at no additional cost, to the latest technology if new applications are introduced during the period that the SA is in effect. These sales do not meet the criteria for gross sales recognition, and thus are recognized on a net basis at the time of sale. Under Net sales recognition, the cost paid to the vendor or third-party service provider is recorded as a reduction to sales, resulting in Net sales being equal to the gross profit on the transaction. The Company’s larger customers are offered the opportunity by certain of its vendors to purchase software licenses and SA under enterprise agreements (“EAs”). Under EAs, customers are considered to be compliant with applicable license requirements for the ensuing year, regardless of changes to their employee base. Customers are charged an annual true-up fee for changes in the number of users over the year. With most EAs, the Company’s vendors will transfer the license and bill the customer directly, paying resellers such as the Company an agency fee or commission on these sales. The Company records these fees as a component of Net sales as earned and there is no corresponding cost of sales amount. In certain instances, the Company bills the customer directly under an EA and accounts for the individual items sold based on the nature of the item. The Company’s vendors typically dictate how the EA will be sold to the customer. The Company also sells some of its products and services as part of bundled contract arrangements containing multiple deliverables, which may include a combination of products and services. For each deliverable that represents a separate unit of accounting, total arrangement consideration is allocated based upon the relative selling prices of each element. The allocated arrangement consideration is recognized as revenue in accordance with the principles described above. Relative selling prices are determined by using vendor specific objective evidence (“VSOE”) if it exists. Otherwise, selling prices are determined using third-party evidence (“TPE”). If neither VSOE or TPE is available, the Company uses its best estimate of selling prices. The Company records freight billed to its customers as Net sales and the related freight costs as a Cost of sales. Deferred revenue includes (i) payments received from customers in advance of providing the product or performing services and (ii) amounts deferred if other conditions of revenue recognition have not been met. The Company performs an analysis of the estimated number of days of sales in-transit to customers at the end of each period based on a weighted-average analysis of commercial delivery terms that includes drop-shipment arrangements. This analysis is the basis upon which the Company estimates the amount of sales in-transit at the end of the period and adjusts revenue and the related costs to reflect only what has been received by the customer. Changes in delivery patterns may result in a different number of business days used in making this adjustment and could have a material impact on the Company’s revenue recognition for the period. Sales Taxes Sales tax amounts collected from customers for remittance to governmental authorities are presented on a net basis in the Consolidated Statements of Operations. Advertising Advertising costs are generally charged to expense in the period incurred. Cooperative reimbursements from vendors are recorded in the period the related advertising expenditure is incurred. The Company classifies vendor consideration as a reduction to Cost of sales. Equity-Based Compensation The Company measures all equity-based payments using a fair-value-based method and records compensation expense over the requisite service period using the straight-line method in its Consolidated Financial Statements. Estimated forfeiture rates have been developed based upon historical experience. Interest Expense Interest expense is recognized in the period incurred at the applicable interest rate in effect. Foreign Currency Translation The Company’s functional currency is the US dollar. The functional currency of the Company’s international operating subsidiaries is generally the same as the corresponding local currency. Assets and liabilities of the international operating subsidiaries are translated at the spot rate in effect at the applicable reporting date. Revenues and expenses of the international operating subsidiaries are translated at the average exchange rates in effect during the applicable period. The resulting foreign currency translation adjustment is recorded as Accumulated other comprehensive loss, which is reflected as a separate component of Stockholders’ equity. Income Taxes Deferred income taxes are provided to reflect the differences between the tax bases of assets and liabilities and their reported amounts in the Consolidated Financial Statements using enacted tax rates in effect for the year in which the differences are expected to reverse. The Company performs an evaluation of the realizability of deferred tax assets on a quarterly basis. This evaluation requires management to make use of estimates and assumptions and considers all positive and negative evidence and factors, such as the scheduled reversal of temporary differences, the mix of earnings in the jurisdictions in which the Company operates, and prudent and feasible tax planning strategies. The Company accounts for unrecognized tax benefits based upon its assessment of whether a tax benefit is more likely than not to be sustained upon examination by tax authorities. The Company reports a liability for unrecognized tax benefits resulting from unrecognized tax benefits taken or expected to be taken in a tax return and recognizes interest and penalties, if any, related to its unrecognized tax benefits in income tax expense. The Tax Cuts and Jobs Act contains a provision which subjects a US parent of a foreign subsidiary to current US tax on its global intangible low-tax income (“GILTI”). The GILTI income is eligible for a deduction, which lowers the effective tax rate to 10.5% for taxable years 2018 through 2025 and 13.125% after 2025. As the Company continues to evaluate its accounting policy with respect to GILTI, the provisional estimates were reported on the basis that GILTI will be accounted for as a period cost when incurred. Accordingly, the Company is not providing deferred taxes for basis differences expected to reverse as GILTI.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2017
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting for Hedging Activities In August 2017, the Financial Accounting Standards Board (the "FASB") issued Accounting Standards Update ("ASU") 2017-12, Derivatives and Hedging (Topic 815), intending to improve the transparency of information included in the financial statements by aligning cash flow and fair value hedge accounting with its risk management activities. The ASU eliminates the requirement to separately measure and report hedge ineffectiveness for cash flow hedges and net investment hedges, and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The ASU also simplifies certain documentation and assessment requirements, and will incorporate new disclosure requirements and amendments to existing disclosures. This ASU is effective for the Company beginning the first quarter of 2019 and allows for early adoption. The Company is currently evaluating the impact the ASU will have on its Consolidated Financial Statements. Accounting for Goodwill Impairment In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment (Topic 350). The amendments in this update eliminate step two of the current two-step process, which requires a hypothetical purchase price allocation when an impairment is determined to have occurred. This ASU 2017-04 is effective for the Company beginning in the first quarter of 2020 and allows for early adoption. The Company elected to early adopt this standard during the third quarter of 2017. The Company will continue to perform the quantitative goodwill impairment evaluation by comparing the fair value of each reporting unit to its carrying amount. Under the new standard, if the Company is required to recognize an impairment charge, the amount of the charge will be measured as the excess of a reporting unit's carrying amount over its fair value, not to exceed the carrying amount of goodwill. The adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements. Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments (Topic 230), providing guidance for eight specific cash flow issues with the objective of reducing the existing diversity in practice. Among the updates, this standard requires cash payments for debt extinguishment costs to be classified as cash outflows from financing activities, which is consistent with the Company's current practice. This ASU is effective for the Company beginning in the first quarter of 2018 and allows for early adoption. The Company elected to early adopt this standard during the third quarter of 2017. The adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements. Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU introduces a new forward-looking approach, based on expected losses, to estimate credit losses on certain types of financial instruments, including trade receivables. The estimate of expected credit losses will require considerations of historical information, current information and reasonable and supportable forecasts. This ASU also expands the disclosure requirements to enable users of financial statements to understand the assumptions, models and methods for estimating expected credit losses. This ASU is effective for the Company beginning in the first quarter of 2020 and allows for early adoption beginning in the first quarter of 2019. The Company is currently evaluating the impact the ASU will have on its Consolidated Financial Statements. Accounting for Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), requiring lessees to recognize assets and liabilities on the balance sheet for the rights and obligations created by long-term leases and to disclose additional quantitative and qualitative information about leasing arrangements. This ASU is effective for the Company beginning in the first quarter of 2019 and allows for early adoption. Although the Company is currently evaluating the provisions of the ASU to determine how it will be affected, the primary impact to the Company of the new ASU will be to record assets and liabilities for current operating leases, which are principally related to the Company’s real estate portfolio. Revenue Recognition In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which, along with amendments issued in 2015 and 2016, will replace most existing revenue recognition guidance under GAAP and eliminate industry-specific guidance. The core principle of the new guidance is that an entity should recognize revenue for the transfer of goods and services equal to an amount it expects to be entitled to receive for those goods and services. The ASU, as amended, will be effective for the Company beginning in the first quarter of 2018. The new guidance permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the cumulative catch-up transition method). The Company established a cross-functional implementation team to analyze the effect of the ASU. The Company utilized a bottom-up approach to analyze the impact of the standard on its contract portfolio by reviewing the current accounting policies and practices to identify potential differences that would result from applying the requirements of the new standard to its revenue contracts. In addition, the Company identified, and is in the process of implementing, appropriate changes to its business processes, systems and controls to support recognition and disclosure under the new standard. The implementation team reports its findings and progress of the project to management and the Audit Committee on a frequent basis. The Company adopted the guidance on January 1, 2018 , and utilized the full retrospective method. The Company has finalized its accounting policies under the new standard and it has determined: • The accounting for bill and hold transactions will result in revenue for certain of those arrangements being recognized earlier than under current GAAP. This change will not materially impact Net sales or Net income; • In certain security software transactions when accompanying third-party delivered software assurance is deemed to be critical or essential to the core functionality of the software license, the Company has determined that the software license and the accompanying third-party delivered software assurance are a single performance obligation. The value of the product is primarily the accompanying support delivered by a third-party and therefore the Company is acting as an agent in these transactions and will recognize them on a net basis. The Company currently recognizes revenue from the software license on a gross basis (i.e., acting as a principal) and accompanying third-party delivered software assurance on a net basis. This change will reduce both Net sales and Cost of sales with no impact on reported Gross profit. • The accounting for revenue related to hardware, software (excluding the above) and services will remain substantially unchanged. The adoption of the ASU is expected to impact the Company’s results as follows: December 31, 2017 December 31, 2016 (in millions) (except per share amounts) As Reported New Revenue Standard Adjustment As Adjusted As Reported New Revenue Standard Adjustment As Adjusted Net sales $ 15,191.5 $ (358.6 ) $ 14,832.9 $ 13,981.9 $ (309.2 ) $ 13,672.7 Gross profit 2,449.9 0.3 $ 2,450.2 2,327.2 1.1 2,328.3 Gross profit margin 16.1 % 40 bps 16.5 % 16.6 % 40 bps 17.0 % Income from operations 866.1 0.4 866.5 819.2 0.8 820.0 Income tax expense (137.3 ) (0.3 ) (137.6 ) (248.0 ) (0.1 ) (248.1 ) Net income $ 523.0 $ 0.1 $ 523.1 $ 424.4 $ 0.7 $ 425.1 Net income per common share Basic $ 3.37 $ — $ 3.37 $ 2.59 $ 0.01 $ 2.60 Diluted $ 3.31 $ — $ 3.31 $ 2.56 $ — $ 2.56 December 31, 2017 December 31, 2016 (in millions) As Reported New Revenue Standard Adjustment As Adjusted (1) As Reported New Revenue Standard Adjustment As Adjusted Accounts receivable $ 2,320.5 $ 8.8 $ 2,329.3 $ 2,168.6 $ 0.3 $ 2,168.9 Merchandise inventory 449.5 (38.0 ) 411.5 452.0 (28.1 ) 423.9 Miscellaneous receivables 336.5 6.5 343.0 234.9 2.6 237.5 Prepaid expenses and other 127.4 40.9 168.3 118.9 35.3 154.2 Total current assets 3,378.1 18.2 3,396.3 3,238.1 10.1 3,248.2 Other assets 40.8 (8.1 ) 32.7 36.0 (0.1 ) 35.9 Total assets 6,956.6 10.1 6,966.7 6,948.4 10.0 6,958.4 Deferred revenue 194.0 (35.2 ) 158.8 172.6 (29.1 ) 143.5 Income tax payable 15.1 1.1 16.2 2.6 0.7 3.3 Other accrued expenses 180.2 41.6 221.8 147.2 36.0 183.2 Total current liabilities 2,514.6 7.5 2,522.1 2,280.7 7.6 2,288.3 Total liabilities 5,973.7 7.5 5,981.1 5,902.9 7.6 5,910.5 Total stockholders’ equity $ 982.9 $ 2.7 $ 985.6 $ 1,045.5 $ 2.4 $ 1,047.9 (1) Amounts may not cross-foot due to rounding. The adoption of the ASU did not impact cash flow provided by operating activities for the years ended December 31, 2017 and 2016.

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisition	Acquisition On August 1, 2015 , the Company completed the acquisition of CDW UK by purchasing the remaining 65% of its outstanding common stock which increased the Company’s ownership interest from 35% to 100% , and provided the Company control. A summary of the total consideration transferred is as follows: (in millions) Acquisition-Date Fair Value Cash $ 291.6 Fair value of CDW common stock (1) 33.2 Fair value of previously held equity investment on the date of acquisition (2) 174.9 Total consideration $ 499.7 (1) The Company issued 2 million shares of CDW common stock. The fair value of the common stock was based on the closing market price on July 31, 2015 , adjusted for the lack of marketability as the shares of CDW common stock issued to certain sellers are subject to a three -year lock up restriction from August 1, 2015 . One of the sellers granted 1 million stock options to certain CDW UK coworkers over his shares of CDW common stock received in the transaction. The fair value of these stock options was $22 million , which has been accounted for as post-combination stock-based compensation and is being amortized over the weighted-average requisite service period of 3.2 years and recorded in Selling and administrative expenses in the Consolidated Statements of Operations. (2) As a result of the Company obtaining control over CDW UK, the Company’s previously held 35% equity investment was remeasured to fair value, resulting in a gain of $98 million included in Gain on remeasurement of equity investment in the Consolidated Statements of Operations. The fair value of the previously held equity investment was determined by management with the assistance of a third party valuation firm, based on information available at the acquisition date. The unaudited pro forma Consolidated Statements of Operations in the table below summarizes the combined results of operations of the Company and CDW UK, as if the acquisition had been completed on January 1, 2015, and gives effect to pro forma events that are factually supportable and directly attributable to the transaction. The unaudited pro forma results reflect adjustments for equity-based compensation, acquisition and integration costs, incremental intangible asset amortization based on the fair values of each identifiable intangible asset, which are subject to change within the measurement period, pre-acquisition equity earnings, the gain on the remeasurement of the Company’s previously held 35% equity method investment, elimination of pre-acquisition intercompany sales transactions and the impacts of certain other pre-acquisition transactions. Pro forma adjustments were tax-effected at the statutory rates within the applicable jurisdictions. This unaudited pro forma information is presented for informational purposes only and may not be indicative of the historical results of operations that would have been obtained if the acquisition had taken place on January 1, 2015, nor the results that may be obtained in the future. This unaudited pro forma information does not reflect future synergies, integration costs or other such costs or savings. The unaudited pro forma Consolidated Statements of Operations is as follows: (in millions) December 31, 2015 Net sales $ 13,507.6 Net income $ 363.7 The unaudited pro forma information above reflects the following adjustments: (i) Excludes acquisition and integration expenses directly related to the transaction. (ii) Includes additional amortization expense related to the fair value of acquired intangibles. (iii) Excludes the gain of resulting from the remeasurement of the Company’s previously held 35% equity investment to fair value upon the completion of the acquisition. (iv) Excludes the Company’s share of net income/loss from its previously held 35% equity investment prior to the completion of the acquisition. (v) Excludes non-cash equity-based compensation related to certain equity awards granted by one of the sellers to CDW UK coworkers in July 2015 prior to the completion of the acquisition. (vi) Includes additional non-cash equity-based compensation related to equity awards granted to CDW UK coworkers after the completion of the acquisition. (vii) Includes the elimination of inter-company sales transactions prior to the completion of the acquisition.

Miscellaneous Receivables

Miscellaneous Receivables	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Miscellaneous Receivables	Miscellaneous Receivables Miscellaneous receivables consist of the following: December 31, (in millions) 2017 2016 Vendor partner receivables $ 279.2 $ 186.6 Other 57.3 48.3 Total $ 336.5 $ 234.9

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consists of the following: December 31, (in millions) 2017 2016 Building and leasehold improvements $ 123.0 $ 120.4 Computer and data processing equipment 116.4 101.7 Machinery and equipment 45.6 43.2 Land 27.7 27.7 Furnitures and fixtures 22.7 23.8 Construction in progress 17.9 20.4 Computer software 9.6 10.8 Property and equipment, gross 362.9 348.0 Less: accumulated depreciation (201.8 ) (184.3 ) Property and equipment, net $ 161.1 $ 163.7 During 2017 , 2016 and 2015 , the Company recorded disposals of $23 million , $50 million and $17 million , respectively, to remove assets that were no longer in use from property and equipment. The Company recorded a pre-tax loss of less than $1 million for all periods for certain disposed assets that were not fully depreciated. Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $40 million , $38 million and $29 million , respectively.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill The changes in goodwill by reportable segment are as follows: (in millions) Corporate Small Business (2) Public Other (4) Consolidated Balance at December 31, 2014 (1) $ 1,045.9 $ 185.9 $ 911.3 $ 74.5 $ 2,217.6 Foreign currency translation — — — (22.4 ) (22.4 ) Acquisition — — — 305.2 305.2 Balance at December 31, 2015 (1) 1,045.9 185.9 911.3 357.3 2,500.4 Foreign currency translation — — — (45.4 ) (45.4 ) CDW Advanced Services Allocation (3) 28.2 — 18.3 (46.5 ) — Balance at December 31, 2016 (1) 1,074.1 185.9 929.6 265.4 2,455.0 Foreign currency translation — — — 24.6 24.6 Balances as of December 31, 2017 (1) $ 1,074.1 $ 185.9 $ 929.6 $ 290.0 $ 2,479.6 (1) Goodwill is net of accumulated impairment losses of $1,571 million , $354 million and $28 million related to the Corporate, Public and Other segments, respectively. (2) Amounts have been recast to present Small Business as its own operating and reportable segment. (3) Effective January 1, 2016, the CDW Advanced Services business is included in the Company's Corporate and Public segments. (4) Other is comprised of Canada and CDW UK operating segments. With the establishment of Small Business as its own reporting unit, the Company performed a quantitative analysis in order to allocate Goodwill between Corporate and Small Business. Based on the results of the quantitative analysis performed as of January 1, 2017, the Company determined that the fair values of Corporate and Small Business reporting units exceeded their carrying values by 227% and 308% , respectively, and no impairment existed. December 1, 2017 Impairment Analysis The Company completed its annual impairment analysis as of December 1, 2017 . For the Corporate, Small Business and UK reporting units, the Company performed a qualitative analysis. The Company determined that it was more-likely-than-not that the individual fair values of the Corporate, Small Business and UK reporting units exceeded the respective carrying values and therefore a quantitative impairment analysis was deemed unnecessary. Although uncertainty regarding the impact of the Referendum on the UK’s Membership of the European Union (“EU”), advising for the exit of the UK from the EU (referred to as “Brexit”) still exists in the current year, the Company does not believe there to be any additional risk that would indicate the quantitative analysis performed in the prior year would have a different result. Therefore, a qualitative analysis was deemed appropriate for the UK reporting unit. The Company performed a quantitative analysis of the Public and Canada reporting units. Based on the results of the quantitative analysis, the Company determined that the fair value of the Public and Canada reporting units exceeded their carrying values by 179% and 153% , respectively, and no impairment existed. December 1, 2016 Impairment Analysis The Company completed its annual impairment analysis as of December 1, 2016 . For the Corporate (which, as of December 1, 2016, included Small Business), Public and Canada reporting units, the Company performed a qualitative analysis. The Company determined that it was more-likely-than-not that the individual fair values of the Corporate, Public and Canada reporting units exceeded the respective carrying values. As a result of this determination, the quantitative impairment analysis was deemed unnecessary. Due to the substantial uncertainty regarding the impact of Brexit, the Company performed a quantitative analysis of the CDW UK reporting unit. Based on the results of the quantitative analysis, the Company determined that the fair value of the CDW UK reporting unit exceeded its carrying value and no impairment existed. Other Intangible Assets A summary of intangible assets is as follows: (in millions) December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Customer relationships and contracts $ 2,106.8 $ (1,490.8 ) $ 616.0 Trade name 422.2 (216.3 ) 205.9 Internally developed software 162.6 (89.6 ) 73.0 Other 2.9 (0.8 ) 2.1 Total $ 2,694.5 $ (1,797.5 ) $ 897.0 December 31, 2016 Customer relationships and contracts $ 2,084.6 $ (1,322.7 ) $ 761.9 Trade name 422.1 (195.2 ) 226.9 Internally developed software 142.6 (77.7 ) 64.9 Other 6.0 (4.1 ) 1.9 Total $ 2,655.3 $ (1,599.7 ) $ 1,055.6 During the years ended December 31, 2017 and 2016 , the Company recorded disposals of $24 million and $29 million , respectively, to remove fully amortized internally developed software assets that were no longer in use. Amortization expense related to intangible assets for the years ended December 31, 2017, 2016 and 2015 was $221 million , $216 million and $199 million , respectively. Estimated future amortization expense related to intangible assets is as follows: (in millions) Years ending December 31, Estimated Future Amortization Expense 2018 $ 219.8 2019 201.4 2020 167.6 2021 72.3 2022 38.4 Thereafter 197.5 Total future amortization expense $ 897.0

Inventory Financing Agreements

Inventory Financing Agreements	12 Months Ended
	Dec. 31, 2017
Inventory Financing Agreements [Abstract]
Inventory Financing Agreements	Inventory Financing Agreements The 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: December 31, (in millions) 2017 2016 Revolving Loan inventory financing agreement (1) $ 480.9 $ 558.3 Other inventory financing agreements (2) 17.1 22.1 Accounts payable-inventory financing $ 498.0 $ 580.4 (1) The Senior Secured Asset-Based Revolving Credit Facility (“Revolving Loan”) 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. (2) The Company also maintains other inventory financing agreements with financial intermediaries to facilitate the purchase of inventory from certain vendors. As of December 31, 2017 and 2016 , amounts collateralized by the inventory purchased under these financing agreements and a second lien on the related accounts receivable were $1 million and $3 million , respectively.

Lease Commitments

Lease Commitments	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Lease Commitments	Lease Commitments The Company is obligated under various non-cancelable operating lease agreements for office facilities that generally provide for minimum rent payments and a proportionate share of operating expenses and property taxes and include certain renewal and expansion options. For the years ended December 31, 2017, 2016 and 2015 , rent expense under these lease arrangements was $29 million , $27 million and $25 million , respectively. Capital leases included in property and equipment are not significant. Future minimum lease payments under non-cancelable operating leases as of December 31, 2017 are as follows: (in millions) Years ending December 31, Future Minimum Lease Payments 2018 $ 22.1 2019 21.8 2020 21.0 2021 14.5 2022 9.0 Thereafter 43.4 Total future minimum lease payments $ 131.8

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [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 LIBOR exceeds 1.5% during the agreement period. The interest rate cap agreements are in effect from January 17, 2017 through December 31, 2018 with a combined notional amount of $1.4 billion . As of December 31, 2017 and 2016 , the interest rate cap agreements had a fair value of $ 5 million and are classified within Other Assets on the Consolidated Balance Sheets. The fair value of the Company’s interest rate cap agreements is 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 details, see Note 10 (Long-Term Debt) . During the first quarter of 2017, the Company designated the interest rate cap agreements as cash flow hedges. The effective portion of changes in the fair value of derivatives that qualify as cash flow hedges is recorded in Accumulated other comprehensive loss and is subsequently reclassified into Interest expense in the period when the hedged forecasted transaction affects earnings. If a derivative is deemed to be ineffective, the ineffective portion of the change in fair value of the derivative is recognized directly into earnings. The Company's interest rate cap agreements were deemed effective during 2017, and the Company expects the derivatives will continue to be effective for the next twelve months. The Company recorded an insignificant gain, net of tax expense, for the effective portion of the interest rate cap agreements into Accumulated other comprehensive loss for the year ended December 31, 2017 . During 2017 , the Company reclassified an insignificant amount from Accumulated other comprehensive loss into Interest expense. The Company expects to reclassify $5 million from Accumulated other comprehensive loss into Interest expense during the next twelve months. Prior to the election of hedge accounting treatment, the Company recognized less than $1 million and $3 million of Interest income during 2017 and 2016 , respectively, in the Company's Consolidated Statement of Operations related to the changes in the fair value of the interest rate cap agreements.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt Long-term debt as of December 31, 2017 is as follows: (dollars in millions) Interest Rate Principal Unamortized Discount and Deferred Financing Costs Total Senior secured asset-based revolving credit facility — % $ — $ — $ — CDW UK revolving credit facility — % — — — Senior secured term loan facility (1) 3.7 % 1,468.0 (2.0 ) 1,466.0 CDW UK term loan 1.9 % 75.7 (1.4 ) 74.3 Senior notes due 2023 5.0 % 525.0 (4.5 ) 520.5 Senior notes due 2024 5.5 % 575.0 (5.2 ) 569.8 Senior notes due 2025 5.0 % 600.0 (7.3 ) 592.7 Other long-term obligations 12.2 — 12.2 Total debt 3,255.9 (20.4 ) 3,235.5 Less current maturities (25.5 ) — (25.5 ) Long-term debt, excluding current maturities $ 3,230.4 $ (20.4 ) $ 3,210.0 (1) The Senior secured term loan facility has a variable interest rate, which has effectively been capped through the use of an interest rate cap (see Note 9 (Financial Instruments) ). The interest rate disclosed represents the variable interest rate in effect as of year ended December 31, 2017 . Long-term debt as of December 31, 2016 is as follows: (dollars in millions) Interest Rate Principal Unamortized Discount and Deferred Financing Costs Total Senior secured asset-based revolving credit facility — % $ — $ — $ — CDW UK revolving credit facility — % — — — Senior secured term loan facility 3.3 % 1,483.0 (14.9 ) 1,468.1 CDW UK term loan 1.8 % 69.1 (1.6 ) 67.5 Senior notes due 2022 6.0 % 600.0 (5.6 ) 594.4 Senior notes due 2023 5.0 % 525.0 (5.3 ) 519.7 Senior notes due 2024 5.5 % 575.0 (6.0 ) 569.0 Other long-term obligations 15.7 — 15.7 Total long-term debt 3,267.8 (33.4 ) 3,234.4 Less current maturities of long-term debt (18.5 ) — (18.5 ) Long-term debt, excluding current maturities $ 3,249.3 $ (33.4 ) $ 3,215.9 Senior Secured Asset-Based Revolving Credit Facility (“Revolving Loan”) As of December 31, 2017 , the Company had no outstanding borrowings under the Revolving Loan, less than $1 million of undrawn letters of credit, $454 million reserved for the floorplan sub-facility and a borrowing base of $1.6 billion , which is based on the amount of eligible inventory and accounts receivable balances as of November 30, 2017. Borrowings under the Revolving Loan are limited by the borrowing base. As of December 31, 2017 , the Company could have borrowed up to an additional $996 million under the Revolving Loan. Borrowings are also limited by a minimum liquidity condition, which provides that, if excess cash availability is less than the lower of (i) $125 million and (ii) the greater of (a) 10.0% of the borrowing base, and (b) $ 100 million , the lenders are not required to lend additional amounts under the Revolving Loan unless the consolidated fixed charge coverage ratio, as defined, is at least 1.00 to 1.00 . Borrowings under the Revolving Loan bear interest at a variable interest rate plus an applicable margin. The interest rate margin is based on one of two indices, either (i) LIBOR or (ii) the Alternate Base Rate (“ABR”), with the ABR being the greater of (a) the prime rate, (b) the federal funds effective rate plus 50 basis points or (c) the one-month LIBOR plus 1.00% . The applicable margin varies ( 1.25% to 1.75% for LIBOR borrowings and 0.25% to 0.75% for ABR borrowings) depending upon average daily excess cash availability under the agreement evidencing the Revolving Loan. On March 31, 2017, the Company amended, extended and increased its Revolving Loan to a five -year, $1.5 billion senior secured asset-based revolving credit facility, with the facility being available to the Company for borrowings, issuance of letters of credit and floorplan financing. The Revolving Loan matures on March 31, 2022. The Revolving Loan replaces the Company’s previous revolving loan credit facility that was to mature on June 6, 2019. The Revolving Loan (i) increases the overall revolving credit facility capacity available to the Company from $ 1.3 billion to $ 1.5 billion , (ii) maintains the maximum aggregate amount of increases that may be made to the revolving credit facility of $300 million , (iii) maintains the fees on the unused portion of the revolving credit facility at 25 basis points, (iv) makes permanent the 25 basis point reduction in the applicable interest rate margin that was previously conditioned on meeting certain credit ratings levels, and (v) maintains the existing inventory floorplan sub-facility. In connection with the amendment of the previous facility, the Company recorded a loss on extinguishment of long-term debt of $ 1 million in the Consolidated Statement of Operations for the year ended December 31, 2017 , representing a write-off of a portion of unamortized deferred financing costs. Fees of $ 4 million related to the Revolving Loan were capitalized as deferred financing costs and are being amortized over the five -year term of the facility on a straight-line basis. These deferred financing costs are recorded in Other assets on the Consolidated Balance Sheets. Senior Secured Term Loan Facility (“Term Loan”) On December 31, 2017 , the outstanding principal amount of the Term Loan was $ 1.5 billion , excluding $ 2 million of deferred financing costs. On February 28, 2017 , the Company amended the Term Loan to reprice the facility, reducing interest rate margins by 25 basis points. Borrowings under the Term Loan bear interest at either (i) the ABR plus a margin or (ii) LIBOR plus a margin, payable quarterly on the last day of each March, June, September and December. The margin is based upon a net leverage ratio as defined in the agreement governing the Term Loan, which is 1.00% for ABR borrowings and 2.00% for LIBOR borrowings as of December 31, 2017 . The Term Loan was issued at par. The Term Loan replaced the prior senior secured term loan facility (the “Prior Term Loan Facility”) that had an outstanding aggregate principal amount of $ 1.5 billion . The Company is required to pay quarterly principal installments equal to 0.25% of the original principal amount of the Prior Term Loan Facility, with the remaining principal amount payable on the maturity date of August 17, 2023 , which was retained from the Prior Term Loan Facility. In connection with this refinancing, the Company recorded a loss on extinguishment of long-term debt of $14 million in the Consolidated Statement of Operations for the year ended December 31, 2017 . This loss represented the write-off of a portion of the unamortized deferred financing costs of $5 million and unamortized discount related to the Prior Term Loan Facility of $9 million . In connection with the issuance of the Term Loan, the Company incurred and recorded $2 million in deferred financing fees, which are recorded as a reduction to the debt and presented in the above table as of December 31, 2017 . CDW UK Term Loan On August 1, 2016, the Company entered into a new five -year £ 56 million ( $76 million at December 31, 2017 ) aggregate principal amount term loan facility (“CDW UK Term Loan”), which replaced the prior senior secured term loan facility (the “Prior CDW UK Term Loan Facility”) that had an outstanding principal amount of £ 56 million . Fees of $1 million were capitalized as deferred financing costs and are being amortized over the term of the loan on a straight-line basis. Commencing during the quarter ending September 30, 2018, the Company is required to make annual principal installments of £ 5 million ( $7 million at December 31, 2017 ), with the remaining principal amount payable on the maturity date of August 1, 2021. Borrowings under the CDW UK Term Loan bear interest at LIBOR plus a margin, payable quarterly on the last day of each March, June, September and December. As of December 31, 2017 , an interest rate of 1.92% was in effect, which represents LIBOR plus a 1.40% margin. In connection with this refinancing, the Prior CDW UK Term Loan Facility was amended to include both the CDW UK Term Loan and a £ 50 million ( $68 million at December 31, 2017 ) revolving credit facility (the “CDW UK Revolving Credit Facility”). As of December 31, 2017 , the Company had no borrowings from the CDW UK Revolving Credit Facility. 6.0% Senior Notes due 2022 (“2022 Senior Notes”) On March 2, 2017 , the proceeds from the issuance of the 2025 Senior Notes, discussed below, along with cash on hand and proceeds from Revolving Loan borrowings, were deposited with the trustee to redeem all of the remaining $600 million aggregate principal amount of the 2022 Senior Notes at a redemption price of 106.182% of the principal amount redeemed, plus accrued and unpaid interest through the date of redemption. The redemption date was April 2, 2017. On the same date, the indenture governing the 2022 Senior Notes was satisfied and discharged. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $43 million in the Consolidated Statement of Operations for the year ended December 31, 2017 . This loss represents $37 million in redemption premium and $6 million for the write-off of the remaining deferred financing costs related to the 2022 Senior Notes. 5.0% Senior Notes due 2023 (“2023 Senior Notes”) At December 31, 2017 , the outstanding principal amount of the 2023 Senior Notes was $525 million . The 2023 Notes will mature on September 1, 2023 and bear interest rate of 5.0% per annum, payable semi-annually on March 1 and September 1 of each year. 5.5% Senior Notes due 2024 (“2024 Senior Notes”) At December 31, 2017 , the outstanding principal amount of the 2024 Senior Notes was $575 million . The 2024 Senior Notes will mature on December 1, 2024 and bear interest at a rate of 5.5% per annum, payable semi-annually on June 1 and December 1 of each year. 5.0% Senior Notes due 2025 (“2025 Senior Notes”) On March 2, 2017 , the Company completed the issuance of $600 million aggregate principal amount of 2025 Senior Notes at par. In connection with the issuance of the 2025 Senior Notes, the Company incurred and recorded $7 million in deferred financing fees, which is recorded as a reduction to the debt and presented in the above table as of December 31, 2017 . At December 31, 2017 , the outstanding principal amount of the 2025 Senior Notes was $600 million . The 2025 Senior Notes will mature on September 1, 2025 and bear interest at a rate of 5.0% per annum, payable semi-annually on March 1 and September 1 of each year. Debt Guarantors, Covenants and Restrictions CDW LLC is the borrower under the Term Loan and Revolving Loan. CDW LLC and CDW Finance Corporation are the co-issuers of the 2023, 2024 and 2025 Senior Notes (“Senior Notes”). The obligations under the Term Loan, the Revolving Loan and the Senior Notes are guaranteed by Parent and each of CDW LLC's direct and indirect, wholly owned, US subsidiaries (the “Guarantors”). The Revolving Loan is collateralized by a first priority interest in inventory (excluding inventory collateralized under the inventory floorplan arrangements as described in Note 7 (Inventory Financing Agreements) ), deposits, and accounts receivable, and a second priority interest in substantially all US assets. The Term Loan is collateralized by a second priority interest in substantially all inventory (excluding inventory collateralized under the inventory floorplan arrangements as described in Note 7 (Inventory Financing Agreements) ), deposits, and accounts receivable, and by a first priority interest in substantially all other U.S. assets. As of December 31, 2017 , the Company remained in compliance with the covenants under its various credit agreements. The Term Loan contains negative covenants that, among other things, place restrictions and limitations on the ability of the Guarantors to dispose of assets, incur additional indebtedness, incur guarantee obligations, prepay other indebtedness, make distributions or other restricted payments, create liens, make equity or debt investments, make acquisitions, engage in mergers or consolidations or engage in certain transactions with affiliates. As of December 31, 2017 , the amount of CDW’s restricted payment capacity under the Term Loan was $1.2 billion . However, the Company is separately permitted to make restricted payments, so long as the total net leverage ratio is less than 3.25 :1.00 on a pro forma basis. The total net leverage ratio was 2.62 :1.00 as of December 31, 2017 . Each of the Senior Notes indentures contain negative covenants that, among other things, place restrictions and limitations on the ability of the Guarantors to enter into sale and lease-back transactions, incur additional secured indebtedness and create liens. The indenture governing each of the Senior Notes do not contain any financial covenants. 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 December 31, 2017 , the amount of restricted payment capacity under the CDW UK Term Loan was £ 73 million ( $98 million at December 31, 2017 ). Long-Term Debt Maturities A summary of Long-term debt maturities is as follows: (in millions) Years ending December 31, Total 2018 $ 25.5 2019 25.7 2020 25.9 2021 70.3 2022 14.9 Thereafter 3,093.6 $ 3,255.9 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 Loan 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 costs, were as follows: December 31, (in millions) 2017 2016 Fair value $ 3,366.5 $ 3,334.8 Carrying value 3,255.9 3,267.8

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On December 22, 2017, the Tax Cuts and Jobs Act was enacted into law. The Tax Cuts and Jobs Act changes several aspects of US federal tax law including: reducing the US corporate income tax rate from 35% to 21% beginning on January 1, 2018; establishing a territorial tax system, which includes a one-time tax on the deemed mandatory repatriation of the Company’s international operations’ unremitted earnings which have not been subject to US tax; imposing a minimum US tax on foreign earnings; providing for the immediate expensing of certain qualified property; and changing the tax treatment of performance based executive compensation and certain employee fringe benefits. US GAAP requires the income tax effects of the Tax Cuts and Jobs Act to be accounted for in the period of enactment. As of December 31, 2017, the Company has not completed its accounting for the income tax effects of the Tax Cuts and Jobs Act; however, it has recorded provisional amounts for the impact of revaluing the deferred tax assets and liabilities, the deemed mandatory repatriation tax on the Company’s international operations’ unremitted earnings which have not been subject to US tax and the state income tax effects related to the change in federal tax law. The Company recorded an income tax benefit of $96 million to reflect the impact of revaluing US deferred tax assets and liabilities to 21%, which is the rate the Company expects the deferred tax assets and liabilities to reverse. The Company has recorded additional federal income tax expense of $20 million to reflect the deemed mandatory repatriation tax on the Company’s international operations’ unremitted earnings which have not been subject to US tax. The mandatory repatriation tax generated excess foreign tax credits of approximately $14 million , which are available for carryforward. The Company does not expect to utilize the foreign tax credits carryforwards prior to their expiration and it has recorded a $14 million valuation allowance against the foreign tax carryforwards. The Company has recorded additional tax expense of less than $1 million for the state income tax impact of the Tax Cuts and Jobs Act. As the Company completes its analysis and refines its calculations of the federal and state income tax impact of the Tax Cuts and Jobs Act, it may need to adjust the measurement of the deferred tax assets and liabilities, update the historical earnings of its UK and Canadian operations which will impact the mandatory repatriation tax, foreign tax credit utilization, carryforwards and valuation allowance, and adjust the state income tax expense. Income before income taxes was taxed under the following jurisdictions: Years Ended December 31, (in millions) 2017 2016 2015 Domestic $ 607.1 $ 635.5 $ 626.4 Foreign 53.2 36.9 20.6 Total $ 660.3 $ 672.4 $ 647.0 Components of Income tax expense (benefit) consist of the following: Years Ended December 31, (in millions) 2017 2016 2015 Current: Federal $ 258.9 $ 295.7 $ 258.5 State 29.8 34.9 28.6 Foreign 21.3 16.8 10.1 Total current 310.0 347.4 297.2 Deferred: Domestic (168.0 ) (90.5 ) (48.5 ) Foreign (4.7 ) (8.9 ) (4.8 ) Total deferred (172.7 ) (99.4 ) (53.3 ) Income tax expense $ 137.3 $ 248.0 $ 243.9 The reconciliation between the statutory tax rate expressed as a percentage of income before income taxes and the effective tax rate is as follows: Years Ended December 31, (dollars in millions) 2017 2016 2015 Statutory federal income tax rate $ 231.1 35.0 % $ 235.4 35.0 % $ 226.4 35.0 % State taxes, net of federal effect (1) 18.3 2.8 17.8 2.6 16.5 2.6 Excess tax benefit of equity awards (36.2 ) (5.5 ) (1.6 ) (0.2 ) — — Effect of rates different than statutory (6.3 ) (1.0 ) (4.5 ) (0.7 ) (1.9 ) (0.3 ) Foreign withholding tax 1.0 0.2 0.8 0.1 3.3 0.5 Effect of UK tax rate change on deferred taxes — — (1.5 ) (0.2 ) (4.0 ) (0.6 ) Effect of US Tax Cuts and Jobs Act on Deferred Taxes and Mandatory Repatriation Tax (75.5 ) (11.4 ) — — — — Other 4.9 0.7 1.6 0.3 3.6 0.5 Effective tax rate $ 137.3 20.8 % $ 248.0 36.9 % $ 243.9 37.7 % (1) The impact of state taxes on excess tax benefits of equity awards and the US Tax Cuts and Jobs Act are presented on the respective separate lines in the effective tax rate reconciliation. The tax effect of temporary differences that give rise to the net deferred income tax liabilities is presented below: December 31, (in millions) 2017 2016 Deferred tax assets: Equity compensation plans $ 18.7 $ 29.2 Payroll and benefits 8.0 22.7 Deferred interest 6.8 13.9 Net operating loss and credit carryforwards, net 28.1 12.7 Rent 7.4 11.0 Accounts receivable 5.4 8.3 Other 8.0 6.2 Trade credits 1.5 0.6 Total deferred tax assets 83.9 104.6 Deferred tax liabilities: Software and intangibles 194.5 337.4 Deferred income 18.6 58.3 International investments 19.2 31.3 Property and equipment 20.4 30.3 Other 12.0 15.3 Total deferred tax liabilities 264.7 472.6 Deferred tax asset valuation allowance 15.5 1.2 Net deferred tax liabilities $ 196.3 $ 369.2 The Company has state and international income tax net operating losses of $29 million , which will expire at various dates from 2025 through 2032 and state and international tax credit carryforwards of $28 million , which expire at various dates from 2019 through 2027. Due to the nature of the CDW UK acquisition, the Company has provided US income taxes of $19 million on the excess of the financial reporting value of the investment over the corresponding tax basis. As the Company continues to evaluate the Tax Cuts and Jobs Act, the Company has made a provisional determination that it is indefinitely reinvested in its UK business, and therefore will not provide for any deferred US taxes on the earnings of the UK business. The Company has also made a provisional determination that it is not permanently reinvested in its Canadian business and therefore has recognized deferred tax liabilities of $3 million as of December 31, 2017 related to withholding taxes on earnings of its Canadian business. In the ordinary course of business, the Company is subject to review by domestic and foreign taxing authorities, including the Internal Revenue Service (“IRS”). In general, the Company is no longer subject to audit by the IRS for tax years through 2013 and state, local or foreign taxing authorities for tax years through 2012. Various other taxing authorities are in the process of auditing income tax returns of the Company and its subsidiaries. The Company does not anticipate that any adjustments from the audits would have a material impact on its consolidated financial position, results of operations or cash flows.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Share Repurchase Program The Company has a share repurchase program under which it may repurchase shares of its common stock in the open market or through privately negotiated other transactions, depending on share price, market conditions and other factors. The share repurchase program does not obligate the Company to repurchase any dollar amount or number of shares, and repurchases may be commenced or suspended from time to time without prior notice. During 2017, the Company repurchased 9 million shares of its common stock for $534 million under the previously announced $750 million share repurchase program. On August 3, 2017, the Company announced that its Board of Directors authorized a $750 million increase to the Company’s share repurchase program. As of December 31, 2017 , the Company has $858 million remaining under this program. Treasury Stock On December 31, 2017, the Company acquired 109,207 shares of its common stock, which are held as treasury stock. The shares were acquired in satisfaction of withholding taxes on behalf of employees under the Performance Share Awards (“PSAs”) program. Refer to Note 13 (Equity-Based Compensation) for additional information on the PSAs.

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2017
Share-based Arrangements with Employees and Nonemployees [Abstract]
Equity-Based Compensation	Equity-Based Compensation Equity-based compensation expense, which is recorded in Selling and administrative expenses in the Consolidated Statements of Operations is as follows: Years Ended December 31, (in millions) 2017 2016 2015 Equity-based compensation expense $ 43.7 $ 39.2 $ 31.2 Income tax benefit (1) (15.3 ) (13.3 ) (10.9 ) Equity-based compensation expense (net of tax) $ 28.4 $ 25.9 $ 20.3 (1) Represents equity-based compensation tax expense at the statutory tax rates. This line does not include any excess tax benefits associated with equity awards separately disclosed in Note 11 (Income Taxes) . The total unrecognized compensation cost related to nonvested awards was $32 million at December 31, 2017 and is expected to be recognized over a weighted-average period of 1.6 years . 2013 Long-Term Incentive Plan The 2013 Long-Term Incentive Plan (“2013 LTIP”) provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock, restricted stock units, bonus stock and performance awards. The maximum aggregate number of shares that may be issued under the 2013 LTIP is 15,500,000 shares of the Company’s common stock, in addition to the 3,798,508 shares of restricted stock granted in exchange for unvested Class B Common Units in connection with the Company’s IPO. As of December 31, 2017 , 6,416,547 shares were available for issuance under the 2013 LTIP which was approved by the Company’s pre-IPO shareholders. Authorized but unissued shares are reserved for issuance in connection with equity-based awards. Stock Options The exercise price of a stock option granted is equal to the fair value of the underlying stock on the date of the grant. Stock options have a contractual term of 10 years and generally vest ratably over three years. To estimate the fair value of options granted, the Company uses the Black-Scholes option pricing model. The weighted-average assumptions used to value the stock options granted were as follows: Years Ended December 31, 2017 2016 2015 Grant date fair value $ 12.27 $ 8.55 $ 11.13 Volatility (1) 22.00 % 25.00 % 30.00 % Risk-free rate (2) 2.08 % 1.47 % 1.75 % Expected dividend yield 1.09 % 1.08 % 0.72 % Expected term (in years) (3) 6.0 6.0 6.0 (1) Based upon an assessment of the two-year and five-year historical volatility and implied volatility for the Company’s selected peer group, adjusted for the Company’s leverage. (2) Based on a composite US Treasury rate. (3) Calculated using the simplified method, which defines the expected term as the average of the option’s contractual term and the option’s weighted-average vesting period. The Company utilizes this method as it has limited historical stock option data that is sufficient to derive a reasonable estimate of the expected stock option term. Stock option activity for the year ended December 31, 2017 was as follows: Options Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value (millions) Outstanding at January 1, 2017 3,781,051 $ 29.36 Granted 1,213,299 58.97 Forfeited/Expired (59,834 ) 45.76 Exercised (1) (476,520 ) 27.37 Outstanding at December 31, 2017 4,457,996 $ 37.41 7.21 $ 143.0 Vested and exercisable at December 31, 2017 2,372,046 $ 25.90 5.97 $ 103.4 Expected to vest at December 31, 2017 2,056,814 $ 50.44 8.61 $ 39.2 (1) The total intrinsic value of stock options exercised during the years ended December 31, 2017, 2016 and 2015 was $17 million , $7 million and $2 million , respectively. Restricted Stock Units (“RSUs”) Restricted stock units represent the right to receive unrestricted shares of the Company’s stock at the time of vesting. RSUs generally cliff-vest at the end of four years. The fair value of RSUs is equal to the closing price of the Company’s common stock on date of grant. RSU activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 1,179,488 $ 19.52 Granted (1) 25,493 58.90 Vested (2) (1,032,821 ) 17.77 Forfeited (41,091 ) 23.00 Nonvested at December 31, 2017 131,069 $ 40.11 (1) The weighted-average grant date fair value of RSUs granted during the years ended December 31, 2017, 2016 and 2015 was $58.90 , $39.82 and $36.24 , respectively. (2) The aggregate fair value of RSUs that vested during the years ended December 31, 2017, 2016 and 2015 was $18 million , $1 million and $1 million , respectively. Performance Share Units (“PSUs”) Performance share units represent the right to receive unrestricted shares of the Company’s stock at the time of vesting. PSUs are granted under the 2013 LTIP which cliff-vest at the end of three years. The percentage of PSUs that shall vest will range from 0% to 200% of the number of PSUs granted based on the Company’s performance against a cumulative adjusted free cash flow measure and cumulative non-GAAP net income per diluted share measure over a three -year performance period. PSU activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 363,947 $ 38.92 Granted (1) 254,451 59.00 Attainment Adjustment (2) 361,880 24.40 Vested (3) (530,569 ) 37.84 Forfeited (30,736 ) 47.28 Nonvested at December 31, 2017 418,973 $ 50.75 (1) The weighted-average grant date fair value of PSUs granted during the years ended December 31, 2017, 2016 and 2015 was $59.00 , $39.91 and $37.83 , respectively. (2) During the year ended December 31, 2017, the attainment on PSUs vested at December 31, 2016 was adjusted to reflect actual performance. The weighted-average grant date fair value of PSUs included in the attainment adjustment is $24.40 . (3) The aggregate fair value of PSUs that vested during the years ended December 31, 2017 and 2016 was $20 million and $9 million , respectively. No PSUs vested during the year ended December 31, 2015. Performance Share Awards (“PSAs”) Performance share awards represent the right to receive unrestricted shares of the Company’s stock at the time of vesting. PSAs are granted under the 2013 LTIP which cliff-vest at the end of three years. The percentage of PSAs that shall vest will range from 0% to 200% of the number of PSAs granted based on the Company’s performance against a cumulative adjusted free cash flow measure and cumulative non-GAAP net income per diluted share measure over a three -year performance period. PSA activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 246,012 $ 38.96 Granted (1) 2,714 — Vested (2) (121,266 ) 37.79 Forfeited (4,993 ) 39.79 Nonvested at December 31, 2017 122,467 $ 40.08 (1) The weighted-average grant date fair value of PSAs granted during the year ended December 31, 2017 was zero as the units granted consisted of only dividends on previously granted units. The weighted-average grant date fair value of PSAs granted during the years ended December 31, 2016 and 2015 was $40.06 and $37.79 , respectively. (2) The aggregate fair value of PSAs that vested during the year ended December 31, 2017 was $5 million . No PSAs vested during the years ended December 31, 2016 and 2015. Restricted Stock (“RSAs”) In connection with the IPO, the Company issued restricted shares of the Company’s common stock to former stockholders of CDW Holdings. These shares are subject to any vesting provisions previously applicable to the restrictions associated with the stock of CDW Holdings. Class B Common Unit holders received 3,798,508 shares of restricted stock with respect to Class B Common Units that had not yet vested at the time of the issuance. RSA activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 26,052 $ 17.00 Granted — — Vested (1) (25,398 ) 17.00 Forfeited (654 ) 17.00 Nonvested at December 31, 2017 — $ — (1) The aggregate fair value of restricted stock that vested during the years ended December 31, 2017, 2016 and 2015 was less than $1 million , $1 million and $3 million , respectively. Equity Awards Granted by Seller of CDW UK The Company issued 1,634,809 shares of CDW common stock as part of the consideration transferred to certain sellers for the acquisition of CDW UK. One of the sellers granted 608,706 stock options to certain CDW UK coworkers over his shares of CDW common stock received in this transaction. The options are not dilutive for purposes of calculating diluted weighted-average shares outstanding as the underlying shares were issued as part of the consideration transferred and are included within basic weighted-average shares outstanding since the acquisition date. The weighted average grant date fair value of the stock options was $22 million or $35.93 per option. The grant date fair value of the options was determined by calculating the fair value of the common stock that was issued which will eventually settle these options. The exercise price of these stock options is $0.01 . The fair value of these stock options has been accounted for as post-combination stock-based compensation, as service is required for the coworkers to retain the awards, and is being amortized over the weighted-average requisite service period. Options that are forfeited prior to vesting will not be available for future option issuances and will revert as consideration to the seller. For further information regarding the acquisition, see Note 3 (Acquisition) .

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
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: Years Ended December 31, (in millions) 2017 2016 2015 Basic weighted-average shares outstanding 155.4 163.6 170.3 Effect of dilutive securities (1) 2.8 2.4 1.5 Diluted weighted-average shares outstanding (2) 158.2 166.0 171.8 (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 less than 1 million potential common shares excluded from diluted weighted-average shares outstanding for the years ended December 31, 2017, 2016 and 2015 , respectively, as their inclusion would have had an anti-dilutive effect.

Coworker Retirement and Other C

Coworker Retirement and Other Compensation Benefits	12 Months Ended
	Dec. 31, 2017
Compensation Related Costs [Abstract]
Coworker Retirement and Other Compensation Benefits	Coworker Retirement and Other Compensation Benefits Profit Sharing Plan and Other Savings Plans The Company has a profit sharing plan that includes a salary reduction feature established under the Internal Revenue Code Section 401(k) covering substantially all coworkers in the US. In addition, coworkers outside the US participate in other savings plans. Company contributions to the profit sharing and other savings plans are made in cash and determined at the discretion of the Board of Directors. For the years ended December 31, 2017, 2016 and 2015 , the amounts expensed for these plans were $20 million , $23 million and $20 million , respectively. Coworker Stock Purchase Plan The Company has a Coworker Stock Purchase Plan (the “CSPP”) that provides the opportunity for eligible coworkers to acquire shares of the Company’s common stock at a 5% discount from the closing market price on the final day of the offering period. There is no compensation expense associated with the CSPP. Restricted Debt Unit Plan On March 10, 2010, the Company established the Restricted Debt Unit Plan (the “RDU Plan”), an unfunded nonqualified deferred compensation plan. Compensation expense related to the RDU Plan was $2 million , $2 million and $5 million for the years ended December 31, 2017, 2016 and 2015 , respectively. On September 15, 2017, the Company settled the RDU Plan. The total payment made on September 15, 2017 was $31 million , which settled the obligation in full.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
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 December 31, 2017 , 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 financial condition and results of operations could be adversely affected in any particular period by the unfavorable resolution of one or more of these proceedings or matters. On October 29, 2015, the Company learned of an investigation by the SEC of the Company’s vendor partner program incentives. On May 19, 2017, the SEC Staff informed the Company that the SEC has concluded its investigation and does not intend to recommend an enforcement action. The investigation did not have any impact on the Company’s financial condition or result of operations other than customary costs related to the Company’s cooperation with the investigation.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The Company held a 35% non-controlling interest in CDW UK until August 1, 2015 when the Company purchased the remaining 65% of its outstanding common stock. The Company recorded $10 million in Net sales to CDW UK during the normal course of business in 2015 prior to the acquisition of CDW UK. On November 30, 2015 , the Company completed a public offering of 9.2 million shares of its common stock by certain selling stockholders, which included 1.2 million shares sold by the selling stockholders to the underwriters pursuant to the grant of an option that was exercised in full. The Company did not receive any proceeds from the sale of these shares. Upon completion of this offering, the Company purchased from the underwriters 1.0 million of the shares of its common stock that were subject to the offering at a price per share equal to the price paid by the underwriters to the selling stockholders in the offering. On August 18, 2015 , the Company completed a public offering of approximately 12.9 million shares of its common stock by certain selling stockholders, which included 1.7 million shares sold by the selling stockholders to the underwriters pursuant to the grant of an option that was exercised in full. The Company did not receive any proceeds from the sale of these shares. Upon completion of this offering, the Company purchased from the underwriters 2.3 million of the shares of its common stock that were subject to the offering at a price per share equal to the price paid by the underwriters to the selling stockholders in the offering. On May 22, 2015 , the Company completed a public offering of 11.5 million shares of its common stock by certain selling stockholders, which included 1.5 million shares sold by the selling stockholders to the underwriters pursuant to the grant of an option that was exercised in full. The Company did not receive any proceeds from the sale of these shares. On May 17, 2015 , the Company entered into a share repurchase agreement with certain selling stockholders affiliated with Madison Dearborn and Providence Equity pursuant to which it repurchased 2.0 million shares of its common stock from such selling stockholders. This share repurchase was effected in a private, non-underwritten transaction for $36.60 per share, which was equal to the per share price paid by the underwriters to the selling stockholders in connection with the public offering completed on May 22, 2015 .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	Segment Information The Company’s segment information is presented in accordance with a “management approach,” which designates the internal reporting used by the Chief Operating Decision-Maker for deciding how to allocate resources and for assessing performance. The Company has three reportable segments: Corporate, which is comprised primarily of private sector business customers with more than 250 employees in the US, Small Business, primarily servicing private sector business customers with up to 250 employees in the US, and Public, which is comprised of government agencies and education and healthcare institutions in the US. The Company has two other operating segments: CDW Canada and CDW UK, both of which do not meet the reportable segment quantitative thresholds and, accordingly, are included in an all other category (“Other”). Effective January 1, 2016, CDW Advanced Services is no longer an operating segment. Its results have been allocated to the Corporate, Small Business and Public segments to align the Company's financial reporting with the manner in which the Chief Operating Decision-Maker assesses performance and makes resource allocation decisions. Segment information reported in prior periods has been reclassified to conform to the current period presentation. The Company has centralized logistics and headquarters functions that provide services to the segments. The logistics function includes purchasing, distribution and fulfillment services to support the Corporate, Small Business and Public segments. As a result, costs and intercompany charges associated with the logistics function are fully allocated to both of these segments based on a percent of Net sales. The centralized headquarters function provides services in areas such as accounting, information technology, marketing, legal and coworker services. Headquarters’ function costs that are not allocated to the segments are included under the heading of “Headquarters” in the tables below. The Company allocates resources to and evaluates performance of its segments based on Net sales, Income from operations and Adjusted EBITDA, a non-GAAP measure as defined in the Company’s credit agreements. However, the Company has concluded that Income from operations is the more useful measure in terms of discussion of operating results, as it is a GAAP measure. Segment information for Total assets and capital expenditures is not presented, as such information is not used in measuring segment performance or allocating resources between segments. Selected Segment Financial Information Information regarding the Company’s segments for the years ended December 31, 2017, 2016 and 2015 is as follows: (in millions) Corporate (1) Small Business (1) Public Other Headquarters Total 2017: Net sales $ 6,347.0 $ 1,246.5 $ 6,037.5 $ 1,560.5 $ — $ 15,191.5 Income (loss) from operations 487.0 74.4 374.0 57.9 (127.2 ) 866.1 Depreciation and amortization expense (83.1 ) (20.7 ) (44.8 ) (30.9 ) (81.4 ) (260.9 ) 2016: Net sales $ 5,889.8 $ 1,140.1 $ 5,589.4 $ 1,362.6 $ — $ 13,981.9 Income (loss) from operations 453.6 68.9 368.0 43.6 (114.9 ) 819.2 Depreciation and amortization expense (82.9 ) (20.6 ) (44.7 ) (32.1 ) (74.2 ) (254.5 ) 2015: Net sales $ 5,878.7 $ 1,089.6 $ 5,183.6 $ 836.8 $ — $ 12,988.7 Income (loss) from operations 432.5 68.3 328.6 27.1 (114.5 ) 742.0 Depreciation and amortization expense (82.6 ) (20.6 ) (44.7 ) (16.2 ) (63.3 ) (227.4 ) (1) Amounts have been recast to present Small Business as its own operating and reportable segment. Geographic Areas and Revenue Mix The Company did not have Net sales to individual countries outside of the US exceeding 10% of the Company’s total Net sales in 2017 , 2016 or 2015 . The Company did not have long-lived assets located in individual countries outside of the US exceeding 10% of the Company’s total long-lived assets as of December 31, 2017 or 2016 . The following table presents Net sales by major category for the years ended December 31, 2017, 2016 and 2015 . Categories are based upon internal classifications. Year Ended December 31, 2017 Year Ended (1) Year Ended (1) Dollars in Millions Percentage of Total Net Sales Dollars in Millions Percentage of Total Net Sales Dollars in Millions Percentage of Total Net Sales Notebooks/Mobile Devices $ 3,490.9 23.1 % $ 2,921.6 20.9 % $ 2,537.3 19.5 % Netcomm Products 2,042.9 13.4 1,958.2 14.0 1,915.0 14.7 Desktops 1,159.4 7.6 1,050.0 7.5 965.6 7.4 Video 1,076.9 7.1 962.1 6.9 853.8 6.6 Enterprise and Data Storage (Including Drives) 1,071.5 7.1 1,053.1 7.5 1,067.2 8.2 Other Hardware 3,100.3 20.4 3,042.6 21.8 2,950.5 22.7 Total Hardware 11,941.9 78.7 10,987.6 78.6 10,289.4 79.1 Software 2,540.1 16.7 2,389.3 17.1 2,152.3 16.6 Services (2) 611.3 4.0 575.1 4.1 467.7 3.6 Other (3) 98.2 0.6 29.9 0.2 79.3 0.7 Total Net sales $ 15,191.5 100.0 % $ 13,981.9 100.0 % $ 12,988.7 100.0 % (1) Amounts have been reclassified for changes in individual product classifications to conform to the presentation for the year ended December 31, 2017 . (2) Certain software and services revenue are recorded on a net basis for accounting purposes, so the category percentage of net revenues is not representative of the category percentage of gross profits. (3) Includes items such as delivery charges to customers and certain commission revenue.

Supplemental Guarantor Informat

Supplemental Guarantor Information	12 Months Ended
	Dec. 31, 2017
Supplemental Guarantor Information [Abstract]
Supplemental Guarantor Information	Supplemental Guarantor Information The 2023 Senior Notes, the 2024 Senior Notes and the 2025 Senior Notes are, and, prior to being redeemed in full, the 2022 Senior Notes were, guaranteed by the Parent and each of CDW LLC’s direct and indirect, 100% owned, domestic subsidiaries (the “Guarantor Subsidiaries”). All guarantees by the Parent and the Guarantor Subsidiaries are and were joint and several, and full and unconditional; provided that guarantees by the Guarantor Subsidiaries (i) are subject to certain customary release provisions contained in the indentures governing the 2023 Senior Notes, the 2024 Senior Notes and the 2025 Senior Notes and (ii) were subject to certain customary release provisions contained in the indenture governing the 2022 Senior Notes until such indenture was satisfied and discharged during 2017. CDW LLC's 100% owned foreign subsidiaries, CDW International Holdings Limited, which is comprised of CDW UK and CDW Canada (together the “Non-Guarantor Subsidiaries”), do not guarantee the debt obligations. CDW LLC and CDW Finance Corporation, as co-issuers, are 100% owned by Parent and each of the Guarantor Subsidiaries and the Non-Guarantor Subsidiaries are, directly or indirectly, 100% owned by CDW LLC. The following tables set forth Condensed Consolidating Balance Sheets as of December 31, 2017 and 2016 , Consolidating Statements of Operations for the years ended December 31, 2017, 2016 and 2015 , Condensed Consolidating Statements of Comprehensive Income for the years ended December 31, 2017, 2016 and 2015 , and Condensed Consolidating Statements of Cash Flows for the years ended December 31, 2017, 2016 and 2015 , in accordance with Rule 3-10 of Regulation S-X. The consolidating financial information includes the accounts of CDW Corporation (the “Parent Guarantor”), which has no independent assets or operations, the accounts of CDW LLC (the “Subsidiary Issuer”), the combined accounts of the Guarantor Subsidiaries, the combined accounts of the Non-Guarantor Subsidiaries, and the accounts of CDW Finance Corporation (the “Co-Issuer”) for the periods indicated. The information was prepared on the same basis as the Company’s Consolidated Financial Statements. Condensed Consolidating Balance Sheet December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Assets Current assets: Cash and cash equivalents $ — $ 113.7 $ — $ 32.4 $ — $ (1.9 ) $ 144.2 Accounts receivable, net — — 2,007.7 312.8 — — 2,320.5 Merchandise inventory — — 375.7 73.8 — — 449.5 Miscellaneous receivables — 103.9 205.0 27.6 — — 336.5 Prepaid expenses and other — 18.0 61.4 48.0 — — 127.4 Total current assets — 235.6 2,649.8 494.6 — (1.9 ) 3,378.1 Property and equipment, net — 95.0 43.5 22.6 — — 161.1 Goodwill — 751.8 1,439.0 288.8 — — 2,479.6 Other intangible assets, net — 280.1 424.5 192.4 — — 897.0 Other assets 1.7 30.7 217.3 2.6 — (211.5 ) 40.8 Investment in and advances to subsidiaries 981.2 3,063.5 — — — (4,044.7 ) — Total Assets $ 982.9 $ 4,456.7 $ 4,774.1 $ 1,001.0 $ — $ (4,258.1 ) $ 6,956.6 Liabilities and Stockholders’ Equity Current liabilities: Accounts payable-trade $ — $ 42.5 $ 1,112.1 $ 165.0 $ — $ (1.9 ) $ 1,317.7 Accounts payable-inventory financing — 1.0 480.9 16.1 — — 498.0 Current maturities of long-term debt — 14.9 3.8 6.8 — — 25.5 Deferred revenue — — 104.5 89.5 — — 194.0 Accrued expenses — 173.3 222.3 83.8 — — 479.4 Total current liabilities — 231.7 1,923.6 361.2 — (1.9 ) 2,514.6 Long-term liabilities: Debt — 3,134.2 8.3 67.5 — — 3,210.0 Deferred income taxes — 66.5 100.1 31.4 — (1.7 ) 196.3 Other liabilities — 43.1 4.6 214.9 — (209.8 ) 52.8 Total long-term liabilities — 3,243.8 113.0 313.8 — (211.5 ) 3,459.1 Total stockholders’ equity 982.9 981.2 2,737.5 326.0 — (4,044.7 ) 982.9 Total Liabilities and Stockholders’ Equity $ 982.9 $ 4,456.7 $ 4,774.1 $ 1,001.0 $ — $ (4,258.1 ) $ 6,956.6 Condensed Consolidating Balance Sheet December 31, 2016 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Assets Current assets: Cash and cash equivalents $ — $ 222.7 $ 3.1 $ 37.9 $ — $ — $ 263.7 Accounts receivable, net — — 1,904.9 263.7 — — 2,168.6 Merchandise inventory — — 390.6 61.4 — — 452.0 Miscellaneous receivables — 92.6 130.1 12.2 — — 234.9 Prepaid expenses and other — 14.3 69.0 35.6 — — 118.9 Total current assets — 329.6 2,497.7 410.8 — — 3,238.1 Property and equipment, net — 105.6 49.3 8.8 — — 163.7 Goodwill — 751.8 1,439.0 264.2 — — 2,455.0 Other intangible assets, net — 291.5 565.1 199.0 — — 1,055.6 Other assets 3.2 19.4 248.2 1.5 — (236.3 ) 36.0 Investment in and advances to subsidiaries 1,042.3 3,026.5 — — — (4,068.8 ) — Total Assets $ 1,045.5 $ 4,524.4 $ 4,799.3 $ 884.3 $ — $ (4,305.1 ) $ 6,948.4 Liabilities and Stockholders’ Equity Current liabilities: Accounts payable-trade $ — $ 25.9 $ 895.3 $ 151.7 $ — $ — $ 1,072.9 Accounts payable-inventory financing — 1.2 559.5 19.7 — — 580.4 Current maturities of long-term debt — 14.9 3.6 — — — 18.5 Deferred revenue — — 100.8 71.8 — — 172.6 Accrued expenses — 173.9 214.8 47.7 — (0.1 ) 436.3 Total current liabilities — 215.9 1,774.0 290.9 — (0.1 ) 2,280.7 Long-term liabilities: Debt — 3,136.3 12.1 67.5 — — 3,215.9 Deferred income taxes — 99.1 205.4 67.9 — (3.2 ) 369.2 Other liabilities — 30.8 3.6 235.7 — (233.0 ) 37.1 Total long-term liabilities — 3,266.2 221.1 371.1 — (236.2 ) 3,622.2 Total stockholders’ equity 1,045.5 1,042.3 2,804.2 222.3 — (4,068.8 ) 1,045.5 Total Liabilities and Stockholders’ Equity $ 1,045.5 $ 4,524.4 $ 4,799.3 $ 884.3 $ — $ (4,305.1 ) $ 6,948.4 Consolidating Statement of Operations Year Ended December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Subsidiaries Co-Issuer Consolidating Adjustments Consolidated Net sales $ — $ — $ 13,631.0 $ 1,560.5 $ — $ — $ 15,191.5 Cost of sales — — 11,436.1 1,305.5 — — 12,741.6 Gross profit — — 2,194.9 255.0 — — 2,449.9 Selling and administrative expenses — 127.2 1,093.1 189.8 — — 1,410.1 Advertising expense — — 166.4 7.3 — — 173.7 Income (loss) from operations — (127.2 ) 935.4 57.9 — — 866.1 Interest (expense) income, net — (148.3 ) 4.1 (6.3 ) — — (150.5 ) Net loss on extinguishments of long-term debt — (57.4 ) — — — — (57.4 ) Other income (expense), net — (0.1 ) 0.7 1.5 — — 2.1 Income (loss) before income taxes — (333.0 ) 940.2 53.1 — — 660.3 Income tax (expense) benefit (0.9 ) 149.9 (269.7 ) (16.6 ) — — (137.3 ) Income (loss) before equity in earnings of subsidiaries (0.9 ) (183.1 ) 670.5 36.5 — — 523.0 Equity in earnings of subsidiaries 523.9 707.0 — — — (1,230.9 ) — Net income $ 523.0 $ 523.9 $ 670.5 $ 36.5 $ — $ (1,230.9 ) $ 523.0 Consolidating Statement of Operations Year Ended December 31, 2016 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Net sales $ — $ — $ 12,619.3 $ 1,362.6 $ — $ — $ 13,981.9 Cost of sales — — 10,514.4 1,140.3 — — 11,654.7 Gross profit — — 2,104.9 222.3 — — 2,327.2 Selling and administrative expenses — 114.8 1,057.4 172.9 — — 1,345.1 Advertising expense — — 157.2 5.7 — — 162.9 Income (loss) from operations — (114.8 ) 890.3 43.7 — — 819.2 Interest (expense) income, net — (145.8 ) 6.7 (7.4 ) — — (146.5 ) Net loss on extinguishments of long-term debt — (2.1 ) — — — — (2.1 ) Other income, net — 0.2 1.0 0.6 — — 1.8 Income (loss) before income taxes — (262.5 ) 898.0 36.9 — — 672.4 Income tax (expense) benefit — 79.9 (319.9 ) (8.0 ) — — (248.0 ) Income (loss) before equity in earnings of subsidiaries — (182.6 ) 578.1 28.9 — — 424.4 Equity in earnings of subsidiaries 424.4 607.0 — — — (1,031.4 ) — Net income $ 424.4 $ 424.4 $ 578.1 $ 28.9 $ — $ (1,031.4 ) $ 424.4 Consolidating Statement of Operations Year Ended December 31, 2015 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Net sales $ — $ — $ 12,151.2 $ 837.5 $ — $ — $ 12,988.7 Cost of sales — — 10,158.6 714.3 — — 10,872.9 Gross profit — — 1,992.6 123.2 — — 2,115.8 Selling and administrative expenses — 114.5 1,020.9 90.6 — — 1,226.0 Advertising expense — — 143.2 4.6 — — 147.8 Income (loss) from operations — (114.5 ) 828.5 28.0 — — 742.0 Interest (expense) income, net — (158.3 ) 2.3 (3.5 ) — — (159.5 ) Net loss on extinguishments of long-term debt — (24.3 ) — — — — (24.3 ) Management fee — 4.2 — (4.2 ) — — — Gain on remeasurement of equity investment — — — 98.1 — — 98.1 Other (expense) income, net — (11.1 ) 1.6 0.2 — — (9.3 ) Income (loss) before income taxes — (304.0 ) 832.4 118.6 — — 647.0 Income tax (expense) benefit — 103.3 (307.2 ) (40.0 ) — — (243.9 ) Income (loss) before equity in earnings of subsidiaries — (200.7 ) 525.2 78.6 — — 403.1 Equity in earnings of subsidiaries 403.1 603.8 — — — (1,006.9 ) — Net income $ 403.1 $ 403.1 $ 525.2 $ 78.6 $ — $ (1,006.9 ) $ 403.1 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Subsidiaries Co-Issuer Consolidating Adjustments Consolidated Comprehensive income $ 566.7 $ 567.6 $ 670.5 $ 80.0 $ — $ (1,318.1 ) $ 566.7 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2016 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Comprehensive income (loss) $ 345.9 $ 345.9 $ 578.1 $ (49.6 ) $ — $ (874.4 ) $ 345.9 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2015 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Comprehensive income $ 358.6 $ 358.6 $ 525.2 $ 34.1 $ — $ (917.9 ) $ 358.6 Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Net cash provided by (used in) operating activities $ 0.6 $ (71.1 ) $ 788.5 $ 52.3 $ — $ 7.4 $ 777.7 Cash flows used in investing activities: Capital expenditures — (55.2 ) (6.3 ) (19.6 ) — — (81.1 ) Net cash used in investing activities — (55.2 ) (6.3 ) (19.6 ) — — (81.1 ) Cash flows (used in) provided by: financing activities: Proceeds from borrowings under revolving credit facility — 1,501.5 — 59.2 — — 1,560.7 Repayments of borrowings under revolving credit facility — (1,501.5 ) — (59.2 ) — — (1,560.7 ) Repayments of long-term debt — (14.9 ) — — — — (14.9 ) Proceeds from issuance of long-term debt — 2,083.0 — — — — 2,083.0 Payments to extinguish long-term debt — (2,121.3 ) — — — — (2,121.3 ) Net change in other long-term obligation — — (3.8 ) — — — (3.8 ) Payment of debt financing costs — (9.6 ) — — — — (9.6 ) Net change in accounts payable-inventory financing — (0.2 ) (78.4 ) (5.4 ) — — (84.0 ) Effective portion of interest rate cap agreements — 0.4 — — — — 0.4 Proceeds from stock option exercises — 13.0 — — — — 13.0 Proceeds from Coworker stock purchase plan — 10.3 — — — — 10.3 Repurchases of common stock (534.0 ) — — — — — (534.0 ) Payment of incentive compensation plan withholding taxes (49.6 ) — — — — — (49.6 ) Dividends (106.9 ) — — — — — (106.9 ) Principal payments under capital lease obligations — — (0.2 ) (1.1 ) — — (1.3 ) Repayment of intercompany loan — — 34.3 (34.3 ) — — — Distributions and advances from (to) affiliates 689.9 56.6 (737.2 ) — — (9.3 ) — Net cash (used in) provided by financing activities (0.6 ) 17.3 (785.3 ) (40.8 ) — (9.3 ) (818.7 ) Effect of exchange rate changes on cash and cash equivalents — — — 2.6 — — 2.6 Net decrease in cash and cash equivalents — (109.0 ) (3.1 ) (5.5 ) — (1.9 ) (119.5 ) Cash and cash equivalents – beginning of period — 222.7 3.1 37.9 — — 263.7 Cash and cash equivalents – end of period $ — $ 113.7 $ — $ 32.4 $ — $ (1.9 ) $ 144.2 Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2016 (in millions) Parent Subsidiary Guarantor Non-Guarantor Co-Issuer Consolidating Consolidated Net cash provided by (used in) operating activities $ — $ (158.5 ) $ 695.5 $ 56.1 $ — $ 10.9 $ 604.0 Cash flows used in investing activities: Capital expenditures — (50.9 ) (7.6 ) (5.0 ) — — (63.5 ) Premium payments on interest rate cap agreements — (2.4 ) — — — — (2.4 ) Net cash used in investing activities — (53.3 ) (7.6 ) (5.0 ) — — (65.9 ) Cash flows (used in) provided by financing activities: Proceeds from borrowings under revolving credit facility — 329.6 — 9.2 — — 338.8 Repayments of borrowings under revolving credit facility — (329.6 ) — (9.2 ) — — (338.8 ) Repayments of long-term debt — (15.2 ) — (5.4 ) — — (20.6 ) Proceeds from issuance of long-term debt — 1,483.0 — — — — 1,483.0 Payments to extinguish long-term debt — (1,490.4 ) — — — — (1,490.4 ) Net change in other long-term obligation — — 15.7 — — — 15.7 Payment of debt financing costs — (4.5 ) — (1.4 ) — — (5.9 ) Net change in accounts payable - inventory financing — 1.5 131.0 11.1 — — 143.6 Proceeds from stock option exercises — 7.4 — — — — 7.4 Proceeds from Coworker Stock Purchase Plan — 9.3 — — — — 9.3 Repurchases of common stock (367.4 ) — — — — — (367.4 ) Dividends (78.7 ) — — — — — (78.7 ) Principal payments under capital lease obligations — — 1.0 (1.6 ) — — (0.6 ) Repayment of intercompany loan — — 40.4 (40.4 ) — — — Distributions and advances from (to) affiliates 446.1 398.3 (872.9 ) — — 28.5 — Net cash (used in) provided by financing activities — 389.4 (684.8 ) (37.7 ) — 28.5 (304.6 ) Effect of exchange rate changes on cash and cash equivalents — — — (7.4 ) — — (7.4 ) Net increase in cash and cash equivalents — 177.6 3.1 6.0 — 39.4 226.1 Cash and cash equivalents—beginning of period — 45.1 — 31.9 — (39.4 ) 37.6 Cash and cash equivalents—end of period $ — $ 222.7 $ 3.1 $ 37.9 $ — $ — $ 263.7 Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2015 (in millions) Parent Subsidiary Guarantor Non-Guarantor Co-Issuer Consolidating Consolidated Net cash provided (used in) by operating activities $ 0.5 $ (18.1 ) $ 350.0 $ 27.9 $ — $ (82.8 ) $ 277.5 Cash flows from investing activities: Capital expenditures — (75.4 ) (11.6 ) (3.1 ) — — (90.1 ) Premium payments on interest rate cap agreements — (0.5 ) — — — — (0.5 ) Acquisition of business, net of cash acquired — — — (263.8 ) — — (263.8 ) Net cash used in investing activities — (75.9 ) (11.6 ) (266.9 ) — — (354.4 ) Cash flows from financing activities: Proceeds from borrowings under revolving credit facility — 314.5 — — — — 314.5 Repayments of borrowings under revolving credit facility — (314.5 ) — — — — (314.5 ) Repayments of long-term debt — (15.4 ) — (17.4 ) — — (32.8 ) Proceeds from issuance of long-term debt — 525.0 — — — — 525.0 Payments to extinguish long-term debt — (525.3 ) — — — — (525.3 ) Payment of debt financing costs — (6.8 ) — — — — (6.8 ) Net change in accounts payable-inventory financing — — 96.1 (0.2 ) — — 95.9 Proceeds from stock option exercises — 2.4 — — — — 2.4 Proceeds from Coworker stock purchase plan — 8.7 — — — — 8.7 Repurchases of common stock (241.3 ) — — — — — (241.3 ) Payment of incentive compensation plan withholding taxes — 0.6 — — — — 0.6 Dividends (52.9 ) — — — — — (52.9 ) Distributions and advances from (to) affiliates 293.7 (196.5 ) (434.5 ) 267.4 — 69.9 — Net cash (used in) provided by financing activities (0.5 ) (207.3 ) (338.4 ) 249.8 — 69.9 (226.5 ) Effect of exchange rate changes on cash and cash equivalents — — — (3.5 ) — — (3.5 ) Net (decrease) increase in cash and cash equivalents — (301.3 ) — 7.3 — (12.9 ) (306.9 ) Cash and cash equivalents – beginning of period — 346.4 — 24.6 — (26.5 ) 344.5 Cash and cash equivalents – end of period $ — $ 45.1 $ — $ 31.9 $ — $ (39.4 ) $ 37.6

Selected Quarterly Financial Re

Selected Quarterly Financial Results (unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Results (unaudited)	Selected Quarterly Financial Results (unaudited) Year Ended December 31, 2017 (1) (in millions, except per-share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Net Sales: Corporate $ 1,476.3 $ 1,630.7 $ 1,598.5 $ 1,641.4 Small Business 298.7 321.5 311.5 314.8 Public: Government 386.9 543.9 606.7 630.0 Education 397.1 712.9 700.7 400.8 Healthcare 392.5 417.3 425.5 423.3 Total Public 1,176.5 1,674.1 1,732.9 1,454.1 Other 373.2 368.1 391.0 428.3 Net sales $ 3,324.7 $ 3,994.4 $ 4,033.9 $ 3,838.6 Gross profit $ 552.6 $ 641.1 $ 642.0 $ 614.4 Income from operations 169.8 231.1 243.7 221.6 Net income (2) 57.6 141.0 129.2 195.2 Basic (3) 0.36 0.90 0.84 1.28 Diluted (3) 0.35 0.89 0.83 1.26 Cash dividends declared per common share $ 0.1600 $ 0.1600 $ 0.1600 $ 0.2100 Year Ended December 31, 2016 (1) (in millions, except per-share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Net Sales: Corporate (4) $ 1,414.9 $ 1,490.8 $ 1,466.4 $ 1,517.7 Small Business (4) 277.4 288.4 282.5 291.8 Public: Government 339.9 456.6 537.5 529.6 Education 341.0 640.0 671.4 365.9 Healthcare 388.5 450.4 431.7 436.8 Total Public 1,069.4 1,547.0 1,640.6 1,332.3 Other 355.0 338.4 318.7 350.5 Net sales $ 3,116.7 $ 3,664.6 $ 3,708.2 $ 3,492.4 Gross profit $ 524.5 $ 610.5 $ 614.3 $ 577.9 Income from operations 161.0 223.5 237.5 197.2 Net income 77.8 117.5 125.9 103.2 Basic (3) 0.47 0.71 0.78 0.64 Diluted (3) 0.46 0.70 0.76 0.63 Cash dividends declared per common share $ 0.1075 $ 0.1075 $ 0.1075 $ 0.1600 (1) Sum of quarters may not agree to reported yearly totals due to rounding. (2) The fourth quarter of 2017 includes the benefit of the Tax Cuts and Jobs Act enacted during 2017. For information regarding the Tax Cuts and Jobs Act, see Note 11 (Income Taxes) . (3) Basic and diluted net income per share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted net income per share. (4) Amounts have been recast to present Small Business as its own operating and reportable segment.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On February 7, 2018 , the Company announced that its Board of Directors has declared a quarterly cash dividend of $0.21 per common share to be paid on March 12, 2018 to all stockholders of record as of the close of business on February 26, 2018 .

Schedule II - Valuation And Qua

Schedule II - Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation And Qualifying Accounts	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS Years ended December 31, 2017, 2016 and 2015 (in millions) Balance at Beginning of Period Charged to Costs and Expenses Deductions Balance at End of Period Allowance for doubtful accounts: Year Ended December 31, 2017 $ 5.9 $ 2.1 $ (1.8 ) $ 6.2 Year Ended December 31, 2016 6.0 2.0 (2.1 ) 5.9 Year Ended December 31, 2015 5.7 4.2 (3.9 ) 6.0 Reserve for sales returns: Year Ended December 31, 2017 $ 6.8 $ 40.6 $ (41.0 ) $ 6.4 Year Ended December 31, 2016 4.9 38.1 (36.2 ) 6.8 Year Ended December 31, 2015 5.1 34.4 (34.6 ) 4.9

Description of Business and S30

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Description of Business	Description of Business CDW Corporation (“Parent”) is a Fortune 500 company with multi-national capabilities and a 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 as described in Note 19 (Supplemental Guarantor Information) and does not hold any material assets or engage in any business activities or operations. In August 2015, the Company completed the acquisition of Kelway TopCo Limited (“Kelway”), a UK-based IT solutions provider with global offerings by purchasing the remaining 65% of its outstanding common stock, which increased the Company’s ownership interest from 35% to 100% and provided the Company control. In 2016 Kelway was rebranded CDW UK.
Basis of Presentation	Basis of Presentation The Consolidated Financial Statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and the rules and regulations of the US Securities and Exchange Commission (“SEC”).
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 GAAP requires management to make use of 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, 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 could differ from those estimates.
Business Combinations	Business Combinations The Company accounts for all business combinations using the acquisition method of accounting, which allocates the fair value of the purchase consideration to the tangible and intangible assets acquired and liabilities assumed based on their estimated fair values. The excess of the purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. When determining the fair values of assets acquired and liabilities assumed, management makes significant estimates and assumptions. The Company may utilize third-party valuation specialists to assist the Company in the allocation. Initial purchase price allocations are subject to revision within the measurement period, not to exceed one year from the date of acquisition. Acquisition-related expenses and transaction costs associated with business combinations are expensed as incurred.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include all deposits in banks and short-term (original maturities of three months or less at the time of purchase), highly liquid investments that are readily convertible to known amounts of cash and are so near maturity that there is insignificant risk of changes in value due to interest rate changes.
Accounts Receivable	Accounts Receivable Trade accounts receivable are recorded at the invoiced amount and typically do not bear interest. The Company provides allowances for doubtful accounts related to accounts receivable for estimated losses resulting from the inability of its customers to make required payments. The Company takes into consideration the overall quality of the receivable portfolio along with specifically-identified customer risks in establishing the allowance.
Merchandise Inventory	Merchandise Inventory Inventory is valued at the lower of cost and net realizable value. Cost is determined using a weighted-average cost method. Price protection is recorded when earned as a reduction to the cost of inventory. The Company decreases the value of inventory for estimated obsolescence equal to the difference between the cost of inventory and the net realizable value, based upon an aging analysis of the inventory on hand, specifically known inventory-related risks, and assumptions about future demand and market conditions.
Miscellaneous Receivables	Miscellaneous Receivables Miscellaneous receivables primarily consist of amounts due from vendors. The Company receives incentives from vendors related to cooperative advertising, volume rebates, bid programs, price protection and other programs. These incentives generally relate to written vendor agreements with specified performance requirements and are recorded as adjustments to Cost of sales or Merchandise inventory, depending on the nature of the incentive.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. The Company calculates depreciation expense using the straight-line method over the estimated useful lives of the assets. Property and equipment are reviewed annually to determine whether there is any impairment. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. If the carrying amount of an asset exceeds its estimated future undiscounted cash flows, an impairment loss is recorded for the excess of the asset’s carrying amount over its fair value. Leasehold improvements are amortized over the shorter of their estimated useful lives or the initial lease term. Expenditures for major renewals and improvements that extend the useful life of property and equipment are capitalized. Expenditures for maintenance and repairs are charged to expense as incurred. The estimated useful lives of property and equipment are as follows: Classification Estimated Machinery and equipment 5 to 10 years Building and leasehold improvements 5 to 25 years Computer and data processing equipment 3 to 5 years Computer software 3 to 5 years Furniture and fixtures 5 to 10 years The Company has asset retirement obligations associated with commitments to return property subject to the terms of operating leases to its original condition upon lease termination.
Equity Investments	Equity Investments If the Company is not required to consolidate its investment in another entity because it does not have control, the Company uses the equity method if it (i) can exercise significant influence over the other entity and (ii) holds common stock of the other entity. Under the equity method, investments are carried at cost, plus or minus the Company’s share of equity in the increases and decreases in the investee’s net assets after the date of acquisition and adjustments for basis differences. The Company’s share of the income or loss of equity method investees is included in Other income (expense), net in the Consolidated Statements of Operations.
Goodwill	Goodwill The Company performs an evaluation of goodwill, utilizing either a qualitative or quantitative impairment test. A qualitative assessment is performed at least on an annual basis to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying value. The Company performs a quantitative impairment test for each reporting unit every three years, or more frequently if circumstances indicate a potential impairment. The annual test for impairment is conducted as of December 1. The Company’s reporting units included in the assessment of potential goodwill impairment are the same as its operating segments. Goodwill is not amortized but is subject to periodic testing for impairment at the reporting unit level. Under a qualitative assessment, the most recent quantitative assessment is used to determine if it is more- likely-than-not that the reporting unit’s goodwill is impaired. As part of this qualitative assessment, the Company assesses relevant events and circumstances including macroeconomic conditions, industry and market conditions, cost factors, overall financial performance, changes in share price and entity-specific events to determine if there is an indication of impairment. Under a quantitative assessment, goodwill impairment is identified by comparing the fair value of a reporting unit to its carrying amount, including goodwill. If the carrying amount of a reporting unit exceeds its fair value, goodwill is considered impaired and an impairment charge is recognized in an amount equal to that excess, not to exceed the carrying amount of goodwill. Fair value of a reporting unit is determined by using a weighted combination of an income approach ( 75% ) and a market approach ( 25% ), as this combination is considered the most indicative of the Company’s fair value in an orderly transaction between market participants. Under the income approach, the Company determines fair value based on estimated future cash flows of a reporting unit, discounted by an estimated weighted-average cost of capital, which reflects the overall level of inherent risk of a reporting unit and the rate of return an outside investor would expect to earn. The estimated future cash flows of each reporting unit are based on internally generated forecasts for the remainder of the respective reporting period and the next five years . The Company uses a range of 2.0 - 3.5% long-term assumed consolidated annual Net sales growth rate for periods after the terminal year. Under the market approach, the Company utilizes valuation multiples derived from publicly available information for guideline companies to provide an indication of how much a knowledgeable investor in the marketplace would be willing to pay for a company. The valuation multiples are applied to the reporting units. Determining the fair value of a reporting unit is judgmental in nature and requires the use of significant estimates and assumptions, including Net sales growth rates, gross profit margins, operating margins, discount rates and future market conditions, among others. Any changes in the judgments, estimates or assumptions used could produce significantly different results.
Intangible Assets	Intangible Assets Intangible assets with determinable lives are amortized on a straight-line basis over their respective estimated useful lives. The cost of computer software developed or obtained for internal use is capitalized and amortized on a straight-line basis over the estimated useful life of the software. Intangible assets are reviewed for impairment when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. If the carrying amount of an asset exceeds its estimated future undiscounted cash flows, an impairment loss is recorded for the excess of the asset’s carrying amount over its fair value. In addition, each quarter, the Company evaluates whether events and circumstances warrant a revision to the remaining estimated useful life of each of these intangible assets. If the Company were to determine that a change to the remaining estimated useful life of an intangible asset was necessary, then the remaining carrying amount of the intangible asset would be amortized prospectively over that revised remaining useful life. The following table shows estimated useful lives of definite-lived intangible assets: Classification Estimated Customer relationships and contracts 3 to 14 years Trade name generally 20 years Internally developed software 3 to 5 years Other 1 to 10 years
Deferred Financing Costs	Deferred Financing Costs Deferred financing costs, such as underwriting, financial advisory, professional fees and other similar fees are capitalized and recognized in Interest expense, net over the estimated life of the related debt instrument using the effective interest method or straight-line method, as applicable. The Company classifies deferred financing costs as a direct deduction from the carrying value of the Long-term debt liability on the Consolidated Balance Sheets, except for deferred financing costs associated with revolving credit facilities which are presented as an asset, within Other assets on the Consolidated Balance Sheets.
Derivative Instruments	Derivative Instruments The Company has interest rate cap agreements for the purpose of hedging its exposure to fluctuations in interest rates. The interest rate cap agreements are designated as cash flow hedges of interest rate risk and recorded at fair value in Other assets on the Consolidated Balance Sheets. The gain or loss on the derivative instruments is reported as a component of Accumulated other comprehensive loss until reclassified to Interest expense in the same period the hedge transaction affects earnings.
Fair Value Measurements	Fair Value Measurements Fair value is defined under GAAP as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A fair value hierarchy has been established for valuation inputs to prioritize the inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market. Each fair value measurement is reported in one of the three levels which is determined by the lowest level input that is significant to the fair value measurement in its entirety. These levels are: Level 1 – observable inputs such as quoted prices for identical instruments traded in active markets. Level 2 – inputs are based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 – inputs are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability. The fair values are therefore determined using model-based techniques that include option pricing models, discounted cash flow models and similar techniques.
Revenue Recognition	Revenue Recognition The Company is a primary distribution channel for a large group of vendors and suppliers, including original equipment manufacturers (“OEMs”), software publishers, wholesale distributors and cloud providers. The Company records revenue from sales transactions when title and risk of loss are passed to the customer, there is persuasive evidence of an arrangement for sale, delivery has occurred and/or services have been rendered, the sales price is fixed or determinable, and collectability is reasonably assured. The Company’s shipping terms typically specify F.O.B. destination, at which time title and risk of loss have passed to the customer. Revenues from the sales of hardware products and software licenses are generally recognized on a gross basis with the selling price to the customer recorded as sales and the acquisition cost of the product recorded as cost of sales. These items can be delivered to customers in a variety of ways, including (i) as physical product shipped from the Company’s warehouse, (ii) via drop-shipment by the vendor or supplier, or (iii) via electronic delivery for software licenses. At the time of sale, the Company records an estimate for sales returns and allowances based on historical experience. The Company’s vendor partners warrant most of the products the Company sells. The Company leverages drop-shipment arrangements with many of its vendors and suppliers to deliver products to its customers without having to physically hold the inventory at its warehouses, thereby increasing efficiency and reducing costs. The Company recognizes revenue for drop-shipment arrangements on a gross basis upon delivery to the customer with contract terms that typically specify F.O.B. destination. Revenue from professional services is either recognized as provided for services billed at an hourly rate, recognized using a percentage of completion model for fixed fee project work or recognized using a proportional performance model for services provided at a fixed fee. Revenues for cloud computing solutions including Software as a Service (“SaaS”) and Infrastructure as a Service (“IaaS”) arrangements with one time invoicing to the customer are recognized at the time of invoice. Revenues for data center services such as managed and remote managed services, server co-location, internet connectivity, data backup and storage, and SaaS and IaaS arrangements where the customer is invoiced over time are recognized over the period service is provided. The Company also sells certain products for which it acts as an agent. Products in this category include the sale of third-party services, warranties, software assurance (“SA”) and third-party hosted SaaS and IaaS arrangements. SA is a product that allows customers to upgrade, at no additional cost, to the latest technology if new applications are introduced during the period that the SA is in effect. These sales do not meet the criteria for gross sales recognition, and thus are recognized on a net basis at the time of sale. Under Net sales recognition, the cost paid to the vendor or third-party service provider is recorded as a reduction to sales, resulting in Net sales being equal to the gross profit on the transaction. The Company’s larger customers are offered the opportunity by certain of its vendors to purchase software licenses and SA under enterprise agreements (“EAs”). Under EAs, customers are considered to be compliant with applicable license requirements for the ensuing year, regardless of changes to their employee base. Customers are charged an annual true-up fee for changes in the number of users over the year. With most EAs, the Company’s vendors will transfer the license and bill the customer directly, paying resellers such as the Company an agency fee or commission on these sales. The Company records these fees as a component of Net sales as earned and there is no corresponding cost of sales amount. In certain instances, the Company bills the customer directly under an EA and accounts for the individual items sold based on the nature of the item. The Company’s vendors typically dictate how the EA will be sold to the customer. The Company also sells some of its products and services as part of bundled contract arrangements containing multiple deliverables, which may include a combination of products and services. For each deliverable that represents a separate unit of accounting, total arrangement consideration is allocated based upon the relative selling prices of each element. The allocated arrangement consideration is recognized as revenue in accordance with the principles described above. Relative selling prices are determined by using vendor specific objective evidence (“VSOE”) if it exists. Otherwise, selling prices are determined using third-party evidence (“TPE”). If neither VSOE or TPE is available, the Company uses its best estimate of selling prices. The Company records freight billed to its customers as Net sales and the related freight costs as a Cost of sales. Deferred revenue includes (i) payments received from customers in advance of providing the product or performing services and (ii) amounts deferred if other conditions of revenue recognition have not been met. The Company performs an analysis of the estimated number of days of sales in-transit to customers at the end of each period based on a weighted-average analysis of commercial delivery terms that includes drop-shipment arrangements. This analysis is the basis upon which the Company estimates the amount of sales in-transit at the end of the period and adjusts revenue and the related costs to reflect only what has been received by the customer. Changes in delivery patterns may result in a different number of business days used in making this adjustment and could have a material impact on the Company’s revenue recognition for the period.
Sales Taxes	Sales Taxes Sales tax amounts collected from customers for remittance to governmental authorities are presented on a net basis in the Consolidated Statements of Operations.
Advertising	Advertising Advertising costs are generally charged to expense in the period incurred. Cooperative reimbursements from vendors are recorded in the period the related advertising expenditure is incurred. The Company classifies vendor consideration as a reduction to Cost of sales.
Equity-Based Compensation	Equity-Based Compensation The Company measures all equity-based payments using a fair-value-based method and records compensation expense over the requisite service period using the straight-line method in its Consolidated Financial Statements. Estimated forfeiture rates have been developed based upon historical experience.
Interest Expense	Interest Expense Interest expense is recognized in the period incurred at the applicable interest rate in effect.
Foreign Currency Translation	Foreign Currency Translation The Company’s functional currency is the US dollar. The functional currency of the Company’s international operating subsidiaries is generally the same as the corresponding local currency. Assets and liabilities of the international operating subsidiaries are translated at the spot rate in effect at the applicable reporting date. Revenues and expenses of the international operating subsidiaries are translated at the average exchange rates in effect during the applicable period. The resulting foreign currency translation adjustment is recorded as Accumulated other comprehensive loss, which is reflected as a separate component of Stockholders’ equity.
Income Taxes	Income Taxes Deferred income taxes are provided to reflect the differences between the tax bases of assets and liabilities and their reported amounts in the Consolidated Financial Statements using enacted tax rates in effect for the year in which the differences are expected to reverse. The Company performs an evaluation of the realizability of deferred tax assets on a quarterly basis. This evaluation requires management to make use of estimates and assumptions and considers all positive and negative evidence and factors, such as the scheduled reversal of temporary differences, the mix of earnings in the jurisdictions in which the Company operates, and prudent and feasible tax planning strategies. The Company accounts for unrecognized tax benefits based upon its assessment of whether a tax benefit is more likely than not to be sustained upon examination by tax authorities. The Company reports a liability for unrecognized tax benefits resulting from unrecognized tax benefits taken or expected to be taken in a tax return and recognizes interest and penalties, if any, related to its unrecognized tax benefits in income tax expense. The Tax Cuts and Jobs Act contains a provision which subjects a US parent of a foreign subsidiary to current US tax on its global intangible low-tax income (“GILTI”). The GILTI income is eligible for a deduction, which lowers the effective tax rate to 10.5% for taxable years 2018 through 2025 and 13.125% after 2025. As the Company continues to evaluate its accounting policy with respect to GILTI, the provisional estimates were reported on the basis that GILTI will be accounted for as a period cost when incurred. Accordingly, the Company is not providing deferred taxes for basis differences expected to reverse as GILTI.
Recent Accounting Pronoucements	Recent Accounting Pronouncements Accounting for Hedging Activities In August 2017, the Financial Accounting Standards Board (the "FASB") issued Accounting Standards Update ("ASU") 2017-12, Derivatives and Hedging (Topic 815), intending to improve the transparency of information included in the financial statements by aligning cash flow and fair value hedge accounting with its risk management activities. The ASU eliminates the requirement to separately measure and report hedge ineffectiveness for cash flow hedges and net investment hedges, and generally requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. The ASU also simplifies certain documentation and assessment requirements, and will incorporate new disclosure requirements and amendments to existing disclosures. This ASU is effective for the Company beginning the first quarter of 2019 and allows for early adoption. The Company is currently evaluating the impact the ASU will have on its Consolidated Financial Statements. Accounting for Goodwill Impairment In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment (Topic 350). The amendments in this update eliminate step two of the current two-step process, which requires a hypothetical purchase price allocation when an impairment is determined to have occurred. This ASU 2017-04 is effective for the Company beginning in the first quarter of 2020 and allows for early adoption. The Company elected to early adopt this standard during the third quarter of 2017. The Company will continue to perform the quantitative goodwill impairment evaluation by comparing the fair value of each reporting unit to its carrying amount. Under the new standard, if the Company is required to recognize an impairment charge, the amount of the charge will be measured as the excess of a reporting unit's carrying amount over its fair value, not to exceed the carrying amount of goodwill. The adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements. Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments (Topic 230), providing guidance for eight specific cash flow issues with the objective of reducing the existing diversity in practice. Among the updates, this standard requires cash payments for debt extinguishment costs to be classified as cash outflows from financing activities, which is consistent with the Company's current practice. This ASU is effective for the Company beginning in the first quarter of 2018 and allows for early adoption. The Company elected to early adopt this standard during the third quarter of 2017. The adoption of this ASU did not have an impact on the Company's Consolidated Financial Statements. Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU introduces a new forward-looking approach, based on expected losses, to estimate credit losses on certain types of financial instruments, including trade receivables. The estimate of expected credit losses will require considerations of historical information, current information and reasonable and supportable forecasts. This ASU also expands the disclosure requirements to enable users of financial statements to understand the assumptions, models and methods for estimating expected credit losses. This ASU is effective for the Company beginning in the first quarter of 2020 and allows for early adoption beginning in the first quarter of 2019. The Company is currently evaluating the impact the ASU will have on its Consolidated Financial Statements. Accounting for Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), requiring lessees to recognize assets and liabilities on the balance sheet for the rights and obligations created by long-term leases and to disclose additional quantitative and qualitative information about leasing arrangements. This ASU is effective for the Company beginning in the first quarter of 2019 and allows for early adoption. Although the Company is currently evaluating the provisions of the ASU to determine how it will be affected, the primary impact to the Company of the new ASU will be to record assets and liabilities for current operating leases, which are principally related to the Company’s real estate portfolio. Revenue Recognition In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), which, along with amendments issued in 2015 and 2016, will replace most existing revenue recognition guidance under GAAP and eliminate industry-specific guidance. The core principle of the new guidance is that an entity should recognize revenue for the transfer of goods and services equal to an amount it expects to be entitled to receive for those goods and services. The ASU, as amended, will be effective for the Company beginning in the first quarter of 2018. The new guidance permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the cumulative catch-up transition method). The Company established a cross-functional implementation team to analyze the effect of the ASU. The Company utilized a bottom-up approach to analyze the impact of the standard on its contract portfolio by reviewing the current accounting policies and practices to identify potential differences that would result from applying the requirements of the new standard to its revenue contracts. In addition, the Company identified, and is in the process of implementing, appropriate changes to its business processes, systems and controls to support recognition and disclosure under the new standard. The implementation team reports its findings and progress of the project to management and the Audit Committee on a frequent basis. The Company adopted the guidance on January 1, 2018 , and utilized the full retrospective method. The Company has finalized its accounting policies under the new standard and it has determined: • The accounting for bill and hold transactions will result in revenue for certain of those arrangements being recognized earlier than under current GAAP. This change will not materially impact Net sales or Net income; • In certain security software transactions when accompanying third-party delivered software assurance is deemed to be critical or essential to the core functionality of the software license, the Company has determined that the software license and the accompanying third-party delivered software assurance are a single performance obligation. The value of the product is primarily the accompanying support delivered by a third-party and therefore the Company is acting as an agent in these transactions and will recognize them on a net basis. The Company currently recognizes revenue from the software license on a gross basis (i.e., acting as a principal) and accompanying third-party delivered software assurance on a net basis. This change will reduce both Net sales and Cost of sales with no impact on reported Gross profit. • The accounting for revenue related to hardware, software (excluding the above) and services will remain substantially unchanged.

Description of Business and S31

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Property, Plant and Equipment	The estimated useful lives of property and equipment are as follows: Classification Estimated Machinery and equipment 5 to 10 years Building and leasehold improvements 5 to 25 years Computer and data processing equipment 3 to 5 years Computer software 3 to 5 years Furniture and fixtures 5 to 10 years Property and equipment consists of the following: December 31, (in millions) 2017 2016 Building and leasehold improvements $ 123.0 $ 120.4 Computer and data processing equipment 116.4 101.7 Machinery and equipment 45.6 43.2 Land 27.7 27.7 Furnitures and fixtures 22.7 23.8 Construction in progress 17.9 20.4 Computer software 9.6 10.8 Property and equipment, gross 362.9 348.0 Less: accumulated depreciation (201.8 ) (184.3 ) Property and equipment, net $ 161.1 $ 163.7
Schedule of Finite-Lived Intangible Assets	The following table shows estimated useful lives of definite-lived intangible assets: Classification Estimated Customer relationships and contracts 3 to 14 years Trade name generally 20 years Internally developed software 3 to 5 years Other 1 to 10 years A summary of intangible assets is as follows: (in millions) December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Customer relationships and contracts $ 2,106.8 $ (1,490.8 ) $ 616.0 Trade name 422.2 (216.3 ) 205.9 Internally developed software 162.6 (89.6 ) 73.0 Other 2.9 (0.8 ) 2.1 Total $ 2,694.5 $ (1,797.5 ) $ 897.0 December 31, 2016 Customer relationships and contracts $ 2,084.6 $ (1,322.7 ) $ 761.9 Trade name 422.1 (195.2 ) 226.9 Internally developed software 142.6 (77.7 ) 64.9 Other 6.0 (4.1 ) 1.9 Total $ 2,655.3 $ (1,599.7 ) $ 1,055.6
Schedule of Accumulated Other Comprehensive Loss	The components of Accumulated other comprehensive loss included in Stockholders’ equity are as follows: Years Ended December 31, (in millions) 2017 2016 2015 Foreign currency translation $ (96.1 ) $ (139.6 ) $ (61.1 ) Unrealized gain from hedge accounting 0.2 — — Accumulated other comprehensive loss $ (95.9 ) $ (139.6 ) $ (61.1 )

Recent Accounting Pronounceme32

Recent Accounting Pronouncements (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Changes and Error Corrections [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The adoption of the ASU is expected to impact the Company’s results as follows: December 31, 2017 December 31, 2016 (in millions) (except per share amounts) As Reported New Revenue Standard Adjustment As Adjusted As Reported New Revenue Standard Adjustment As Adjusted Net sales $ 15,191.5 $ (358.6 ) $ 14,832.9 $ 13,981.9 $ (309.2 ) $ 13,672.7 Gross profit 2,449.9 0.3 $ 2,450.2 2,327.2 1.1 2,328.3 Gross profit margin 16.1 % 40 bps 16.5 % 16.6 % 40 bps 17.0 % Income from operations 866.1 0.4 866.5 819.2 0.8 820.0 Income tax expense (137.3 ) (0.3 ) (137.6 ) (248.0 ) (0.1 ) (248.1 ) Net income $ 523.0 $ 0.1 $ 523.1 $ 424.4 $ 0.7 $ 425.1 Net income per common share Basic $ 3.37 $ — $ 3.37 $ 2.59 $ 0.01 $ 2.60 Diluted $ 3.31 $ — $ 3.31 $ 2.56 $ — $ 2.56 December 31, 2017 December 31, 2016 (in millions) As Reported New Revenue Standard Adjustment As Adjusted (1) As Reported New Revenue Standard Adjustment As Adjusted Accounts receivable $ 2,320.5 $ 8.8 $ 2,329.3 $ 2,168.6 $ 0.3 $ 2,168.9 Merchandise inventory 449.5 (38.0 ) 411.5 452.0 (28.1 ) 423.9 Miscellaneous receivables 336.5 6.5 343.0 234.9 2.6 237.5 Prepaid expenses and other 127.4 40.9 168.3 118.9 35.3 154.2 Total current assets 3,378.1 18.2 3,396.3 3,238.1 10.1 3,248.2 Other assets 40.8 (8.1 ) 32.7 36.0 (0.1 ) 35.9 Total assets 6,956.6 10.1 6,966.7 6,948.4 10.0 6,958.4 Deferred revenue 194.0 (35.2 ) 158.8 172.6 (29.1 ) 143.5 Income tax payable 15.1 1.1 16.2 2.6 0.7 3.3 Other accrued expenses 180.2 41.6 221.8 147.2 36.0 183.2 Total current liabilities 2,514.6 7.5 2,522.1 2,280.7 7.6 2,288.3 Total liabilities 5,973.7 7.5 5,981.1 5,902.9 7.6 5,910.5 Total stockholders’ equity $ 982.9 $ 2.7 $ 985.6 $ 1,045.5 $ 2.4 $ 1,047.9 (1) Amounts may not cross-foot due to rounding.

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	A summary of the total consideration transferred is as follows: (in millions) Acquisition-Date Fair Value Cash $ 291.6 Fair value of CDW common stock (1) 33.2 Fair value of previously held equity investment on the date of acquisition (2) 174.9 Total consideration $ 499.7 (1) The Company issued 2 million shares of CDW common stock. The fair value of the common stock was based on the closing market price on July 31, 2015 , adjusted for the lack of marketability as the shares of CDW common stock issued to certain sellers are subject to a three -year lock up restriction from August 1, 2015 . One of the sellers granted 1 million stock options to certain CDW UK coworkers over his shares of CDW common stock received in the transaction. The fair value of these stock options was $22 million , which has been accounted for as post-combination stock-based compensation and is being amortized over the weighted-average requisite service period of 3.2 years and recorded in Selling and administrative expenses in the Consolidated Statements of Operations. (2) As a result of the Company obtaining control over CDW UK, the Company’s previously held 35% equity investment was remeasured to fair value, resulting in a gain of $98 million included in Gain on remeasurement of equity investment in the Consolidated Statements of Operations. The fair value of the previously held equity investment was determined by management with the assistance of a third party valuation firm, based on information available at the acquisition date.
Business Acquisition, Pro Forma Information	The unaudited pro forma Consolidated Statements of Operations is as follows: (in millions) December 31, 2015 Net sales $ 13,507.6 Net income $ 363.7 The unaudited pro forma information above reflects the following adjustments: (i) Excludes acquisition and integration expenses directly related to the transaction. (ii) Includes additional amortization expense related to the fair value of acquired intangibles. (iii) Excludes the gain of resulting from the remeasurement of the Company’s previously held 35% equity investment to fair value upon the completion of the acquisition. (iv) Excludes the Company’s share of net income/loss from its previously held 35% equity investment prior to the completion of the acquisition. (v) Excludes non-cash equity-based compensation related to certain equity awards granted by one of the sellers to CDW UK coworkers in July 2015 prior to the completion of the acquisition. (vi) Includes additional non-cash equity-based compensation related to equity awards granted to CDW UK coworkers after the completion of the acquisition. (vii) Includes the elimination of inter-company sales transactions prior to the completion of the acquisition.

Miscellaneous Receivables (Tabl

Miscellaneous Receivables (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Schedule of Miscellaneous Receivables	Miscellaneous receivables consist of the following: December 31, (in millions) 2017 2016 Vendor partner receivables $ 279.2 $ 186.6 Other 57.3 48.3 Total $ 336.5 $ 234.9

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The estimated useful lives of property and equipment are as follows: Classification Estimated Machinery and equipment 5 to 10 years Building and leasehold improvements 5 to 25 years Computer and data processing equipment 3 to 5 years Computer software 3 to 5 years Furniture and fixtures 5 to 10 years Property and equipment consists of the following: December 31, (in millions) 2017 2016 Building and leasehold improvements $ 123.0 $ 120.4 Computer and data processing equipment 116.4 101.7 Machinery and equipment 45.6 43.2 Land 27.7 27.7 Furnitures and fixtures 22.7 23.8 Construction in progress 17.9 20.4 Computer software 9.6 10.8 Property and equipment, gross 362.9 348.0 Less: accumulated depreciation (201.8 ) (184.3 ) Property and equipment, net $ 161.1 $ 163.7

Goodwill and Other Intangible36

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in goodwill by reportable segment are as follows: (in millions) Corporate Small Business (2) Public Other (4) Consolidated Balance at December 31, 2014 (1) $ 1,045.9 $ 185.9 $ 911.3 $ 74.5 $ 2,217.6 Foreign currency translation — — — (22.4 ) (22.4 ) Acquisition — — — 305.2 305.2 Balance at December 31, 2015 (1) 1,045.9 185.9 911.3 357.3 2,500.4 Foreign currency translation — — — (45.4 ) (45.4 ) CDW Advanced Services Allocation (3) 28.2 — 18.3 (46.5 ) — Balance at December 31, 2016 (1) 1,074.1 185.9 929.6 265.4 2,455.0 Foreign currency translation — — — 24.6 24.6 Balances as of December 31, 2017 (1) $ 1,074.1 $ 185.9 $ 929.6 $ 290.0 $ 2,479.6 (1) Goodwill is net of accumulated impairment losses of $1,571 million , $354 million and $28 million related to the Corporate, Public and Other segments, respectively. (2) Amounts have been recast to present Small Business as its own operating and reportable segment. (3) Effective January 1, 2016, the CDW Advanced Services business is included in the Company's Corporate and Public segments. (4) Other is comprised of Canada and CDW UK operating segments.
Schedule of Finite-Lived Intangible Assets	The following table shows estimated useful lives of definite-lived intangible assets: Classification Estimated Customer relationships and contracts 3 to 14 years Trade name generally 20 years Internally developed software 3 to 5 years Other 1 to 10 years A summary of intangible assets is as follows: (in millions) December 31, 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Customer relationships and contracts $ 2,106.8 $ (1,490.8 ) $ 616.0 Trade name 422.2 (216.3 ) 205.9 Internally developed software 162.6 (89.6 ) 73.0 Other 2.9 (0.8 ) 2.1 Total $ 2,694.5 $ (1,797.5 ) $ 897.0 December 31, 2016 Customer relationships and contracts $ 2,084.6 $ (1,322.7 ) $ 761.9 Trade name 422.1 (195.2 ) 226.9 Internally developed software 142.6 (77.7 ) 64.9 Other 6.0 (4.1 ) 1.9 Total $ 2,655.3 $ (1,599.7 ) $ 1,055.6
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated future amortization expense related to intangible assets is as follows: (in millions) Years ending December 31, Estimated Future Amortization Expense 2018 $ 219.8 2019 201.4 2020 167.6 2021 72.3 2022 38.4 Thereafter 197.5 Total future amortization expense $ 897.0

Inventory Financing Agreements

Inventory Financing Agreements (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Financing Agreements [Abstract]
Inventory Financing Agreements	Amounts included in accounts payable-inventory financing are as follows: December 31, (in millions) 2017 2016 Revolving Loan inventory financing agreement (1) $ 480.9 $ 558.3 Other inventory financing agreements (2) 17.1 22.1 Accounts payable-inventory financing $ 498.0 $ 580.4 (1) The Senior Secured Asset-Based Revolving Credit Facility (“Revolving Loan”) 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. (2) The Company also maintains other inventory financing agreements with financial intermediaries to facilitate the purchase of inventory from certain vendors. As of December 31, 2017 and 2016 , amounts collateralized by the inventory purchased under these financing agreements and a second lien on the related accounts receivable were $1 million and $3 million , respectively.

Lease Commitments (Tables)

Lease Commitments (Tables)	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Operating Leases of Lessee Disclosure	Future minimum lease payments under non-cancelable operating leases as of December 31, 2017 are as follows: (in millions) Years ending December 31, Future Minimum Lease Payments 2018 $ 22.1 2019 21.8 2020 21.0 2021 14.5 2022 9.0 Thereafter 43.4 Total future minimum lease payments $ 131.8

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Carrying Value of Long-Term Debt	Long-term debt as of December 31, 2017 is as follows: (dollars in millions) Interest Rate Principal Unamortized Discount and Deferred Financing Costs Total Senior secured asset-based revolving credit facility — % $ — $ — $ — CDW UK revolving credit facility — % — — — Senior secured term loan facility (1) 3.7 % 1,468.0 (2.0 ) 1,466.0 CDW UK term loan 1.9 % 75.7 (1.4 ) 74.3 Senior notes due 2023 5.0 % 525.0 (4.5 ) 520.5 Senior notes due 2024 5.5 % 575.0 (5.2 ) 569.8 Senior notes due 2025 5.0 % 600.0 (7.3 ) 592.7 Other long-term obligations 12.2 — 12.2 Total debt 3,255.9 (20.4 ) 3,235.5 Less current maturities (25.5 ) — (25.5 ) Long-term debt, excluding current maturities $ 3,230.4 $ (20.4 ) $ 3,210.0 (1) The Senior secured term loan facility has a variable interest rate, which has effectively been capped through the use of an interest rate cap (see Note 9 (Financial Instruments) ). The interest rate disclosed represents the variable interest rate in effect as of year ended December 31, 2017 . Long-term debt as of December 31, 2016 is as follows: (dollars in millions) Interest Rate Principal Unamortized Discount and Deferred Financing Costs Total Senior secured asset-based revolving credit facility — % $ — $ — $ — CDW UK revolving credit facility — % — — — Senior secured term loan facility 3.3 % 1,483.0 (14.9 ) 1,468.1 CDW UK term loan 1.8 % 69.1 (1.6 ) 67.5 Senior notes due 2022 6.0 % 600.0 (5.6 ) 594.4 Senior notes due 2023 5.0 % 525.0 (5.3 ) 519.7 Senior notes due 2024 5.5 % 575.0 (6.0 ) 569.0 Other long-term obligations 15.7 — 15.7 Total long-term debt 3,267.8 (33.4 ) 3,234.4 Less current maturities of long-term debt (18.5 ) — (18.5 ) Long-term debt, excluding current maturities $ 3,249.3 $ (33.4 ) $ 3,215.9
Schedule of Long-term Debt Maturities	A summary of Long-term debt maturities is as follows: (in millions) Years ending December 31, Total 2018 $ 25.5 2019 25.7 2020 25.9 2021 70.3 2022 14.9 Thereafter 3,093.6 $ 3,255.9
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments	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 costs, were as follows: December 31, (in millions) 2017 2016 Fair value $ 3,366.5 $ 3,334.8 Carrying value 3,255.9 3,267.8

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Income before income taxes was taxed under the following jurisdictions: Years Ended December 31, (in millions) 2017 2016 2015 Domestic $ 607.1 $ 635.5 $ 626.4 Foreign 53.2 36.9 20.6 Total $ 660.3 $ 672.4 $ 647.0
Schedule of Components of Income Tax Expense (Benefit)	Components of Income tax expense (benefit) consist of the following: Years Ended December 31, (in millions) 2017 2016 2015 Current: Federal $ 258.9 $ 295.7 $ 258.5 State 29.8 34.9 28.6 Foreign 21.3 16.8 10.1 Total current 310.0 347.4 297.2 Deferred: Domestic (168.0 ) (90.5 ) (48.5 ) Foreign (4.7 ) (8.9 ) (4.8 ) Total deferred (172.7 ) (99.4 ) (53.3 ) Income tax expense $ 137.3 $ 248.0 $ 243.9
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation between the statutory tax rate expressed as a percentage of income before income taxes and the effective tax rate is as follows: Years Ended December 31, (dollars in millions) 2017 2016 2015 Statutory federal income tax rate $ 231.1 35.0 % $ 235.4 35.0 % $ 226.4 35.0 % State taxes, net of federal effect (1) 18.3 2.8 17.8 2.6 16.5 2.6 Excess tax benefit of equity awards (36.2 ) (5.5 ) (1.6 ) (0.2 ) — — Effect of rates different than statutory (6.3 ) (1.0 ) (4.5 ) (0.7 ) (1.9 ) (0.3 ) Foreign withholding tax 1.0 0.2 0.8 0.1 3.3 0.5 Effect of UK tax rate change on deferred taxes — — (1.5 ) (0.2 ) (4.0 ) (0.6 ) Effect of US Tax Cuts and Jobs Act on Deferred Taxes and Mandatory Repatriation Tax (75.5 ) (11.4 ) — — — — Other 4.9 0.7 1.6 0.3 3.6 0.5 Effective tax rate $ 137.3 20.8 % $ 248.0 36.9 % $ 243.9 37.7 % (1) The impact of state taxes on excess tax benefits of equity awards and the US Tax Cuts and Jobs Act are presented on the respective separate lines in the effective tax rate reconciliation.
Schedule of Deferred Tax Assets and Liabilities	The tax effect of temporary differences that give rise to the net deferred income tax liabilities is presented below: December 31, (in millions) 2017 2016 Deferred tax assets: Equity compensation plans $ 18.7 $ 29.2 Payroll and benefits 8.0 22.7 Deferred interest 6.8 13.9 Net operating loss and credit carryforwards, net 28.1 12.7 Rent 7.4 11.0 Accounts receivable 5.4 8.3 Other 8.0 6.2 Trade credits 1.5 0.6 Total deferred tax assets 83.9 104.6 Deferred tax liabilities: Software and intangibles 194.5 337.4 Deferred income 18.6 58.3 International investments 19.2 31.3 Property and equipment 20.4 30.3 Other 12.0 15.3 Total deferred tax liabilities 264.7 472.6 Deferred tax asset valuation allowance 15.5 1.2 Net deferred tax liabilities $ 196.3 $ 369.2

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Share-based Arrangements with Employees and Nonemployees [Abstract]
Schedule Equity-Based Compensation Expense	Equity-based compensation expense, which is recorded in Selling and administrative expenses in the Consolidated Statements of Operations is as follows: Years Ended December 31, (in millions) 2017 2016 2015 Equity-based compensation expense $ 43.7 $ 39.2 $ 31.2 Income tax benefit (1) (15.3 ) (13.3 ) (10.9 ) Equity-based compensation expense (net of tax) $ 28.4 $ 25.9 $ 20.3 (1) Represents equity-based compensation tax expense at the statutory tax rates. This line does not include any excess tax benefits associated with equity awards separately disclosed in Note 11 (Income Taxes) .
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The weighted-average assumptions used to value the stock options granted were as follows: Years Ended December 31, 2017 2016 2015 Grant date fair value $ 12.27 $ 8.55 $ 11.13 Volatility (1) 22.00 % 25.00 % 30.00 % Risk-free rate (2) 2.08 % 1.47 % 1.75 % Expected dividend yield 1.09 % 1.08 % 0.72 % Expected term (in years) (3) 6.0 6.0 6.0 (1) Based upon an assessment of the two-year and five-year historical volatility and implied volatility for the Company’s selected peer group, adjusted for the Company’s leverage. (2) Based on a composite US Treasury rate. (3) Calculated using the simplified method, which defines the expected term as the average of the option’s contractual term and the option’s weighted-average vesting period. The Company utilizes this method as it has limited historical stock option data that is sufficient to derive a reasonable estimate of the expected stock option term.
Schedule of Stock Options Roll Forward	Stock option activity for the year ended December 31, 2017 was as follows: Options Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (years) Aggregate Intrinsic Value (millions) Outstanding at January 1, 2017 3,781,051 $ 29.36 Granted 1,213,299 58.97 Forfeited/Expired (59,834 ) 45.76 Exercised (1) (476,520 ) 27.37 Outstanding at December 31, 2017 4,457,996 $ 37.41 7.21 $ 143.0 Vested and exercisable at December 31, 2017 2,372,046 $ 25.90 5.97 $ 103.4 Expected to vest at December 31, 2017 2,056,814 $ 50.44 8.61 $ 39.2 (1) The total intrinsic value of stock options exercised during the years ended December 31, 2017, 2016 and 2015 was $17 million , $7 million and $2 million , respectively.
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity	RSU activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 1,179,488 $ 19.52 Granted (1) 25,493 58.90 Vested (2) (1,032,821 ) 17.77 Forfeited (41,091 ) 23.00 Nonvested at December 31, 2017 131,069 $ 40.11 (1) The weighted-average grant date fair value of RSUs granted during the years ended December 31, 2017, 2016 and 2015 was $58.90 , $39.82 and $36.24 , respectively. (2) The aggregate fair value of RSUs that vested during the years ended December 31, 2017, 2016 and 2015 was $18 million , $1 million and $1 million , respectively.
Schedule of Nonvested Performance-based Units Activity	PSU activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 363,947 $ 38.92 Granted (1) 254,451 59.00 Attainment Adjustment (2) 361,880 24.40 Vested (3) (530,569 ) 37.84 Forfeited (30,736 ) 47.28 Nonvested at December 31, 2017 418,973 $ 50.75 (1) The weighted-average grant date fair value of PSUs granted during the years ended December 31, 2017, 2016 and 2015 was $59.00 , $39.91 and $37.83 , respectively. (2) During the year ended December 31, 2017, the attainment on PSUs vested at December 31, 2016 was adjusted to reflect actual performance. The weighted-average grant date fair value of PSUs included in the attainment adjustment is $24.40 . (3) The aggregate fair value of PSUs that vested during the years ended December 31, 2017 and 2016 was $20 million and $9 million , respectively. No PSUs vested during the year ended December 31, 2015.
Share-based Compensation, Performance Shares Award Nonvested Activity	PSA activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 246,012 $ 38.96 Granted (1) 2,714 — Vested (2) (121,266 ) 37.79 Forfeited (4,993 ) 39.79 Nonvested at December 31, 2017 122,467 $ 40.08 (1) The weighted-average grant date fair value of PSAs granted during the year ended December 31, 2017 was zero as the units granted consisted of only dividends on previously granted units. The weighted-average grant date fair value of PSAs granted during the years ended December 31, 2016 and 2015 was $40.06 and $37.79 , respectively. (2) The aggregate fair value of PSAs that vested during the year ended December 31, 2017 was $5 million . No PSAs vested during the years ended December 31, 2016 and 2015.
Nonvested Restricted Stock Shares Activity	RSA activity for the year ended December 31, 2017 was as follows: Number of Units Weighted-Average Grant-Date Fair Value Nonvested at January 1, 2017 26,052 $ 17.00 Granted — — Vested (1) (25,398 ) 17.00 Forfeited (654 ) 17.00 Nonvested at December 31, 2017 — $ — (1) The aggregate fair value of restricted stock that vested during the years ended December 31, 2017, 2016 and 2015 was less than $1 million , $1 million and $3 million , respectively.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
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: Years Ended December 31, (in millions) 2017 2016 2015 Basic weighted-average shares outstanding 155.4 163.6 170.3 Effect of dilutive securities (1) 2.8 2.4 1.5 Diluted weighted-average shares outstanding (2) 158.2 166.0 171.8 (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 less than 1 million potential common shares excluded from diluted weighted-average shares outstanding for the years ended December 31, 2017, 2016 and 2015 , respectively, as their inclusion would have had an anti-dilutive effect.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Information regarding the Company’s segments for the years ended December 31, 2017, 2016 and 2015 is as follows: (in millions) Corporate (1) Small Business (1) Public Other Headquarters Total 2017: Net sales $ 6,347.0 $ 1,246.5 $ 6,037.5 $ 1,560.5 $ — $ 15,191.5 Income (loss) from operations 487.0 74.4 374.0 57.9 (127.2 ) 866.1 Depreciation and amortization expense (83.1 ) (20.7 ) (44.8 ) (30.9 ) (81.4 ) (260.9 ) 2016: Net sales $ 5,889.8 $ 1,140.1 $ 5,589.4 $ 1,362.6 $ — $ 13,981.9 Income (loss) from operations 453.6 68.9 368.0 43.6 (114.9 ) 819.2 Depreciation and amortization expense (82.9 ) (20.6 ) (44.7 ) (32.1 ) (74.2 ) (254.5 ) 2015: Net sales $ 5,878.7 $ 1,089.6 $ 5,183.6 $ 836.8 $ — $ 12,988.7 Income (loss) from operations 432.5 68.3 328.6 27.1 (114.5 ) 742.0 Depreciation and amortization expense (82.6 ) (20.6 ) (44.7 ) (16.2 ) (63.3 ) (227.4 ) (1) Amounts have been recast to present Small Business as its own operating and reportable segment.
Revenue from External Customers by Products and Services	The following table presents Net sales by major category for the years ended December 31, 2017, 2016 and 2015 . Categories are based upon internal classifications. Year Ended December 31, 2017 Year Ended (1) Year Ended (1) Dollars in Millions Percentage of Total Net Sales Dollars in Millions Percentage of Total Net Sales Dollars in Millions Percentage of Total Net Sales Notebooks/Mobile Devices $ 3,490.9 23.1 % $ 2,921.6 20.9 % $ 2,537.3 19.5 % Netcomm Products 2,042.9 13.4 1,958.2 14.0 1,915.0 14.7 Desktops 1,159.4 7.6 1,050.0 7.5 965.6 7.4 Video 1,076.9 7.1 962.1 6.9 853.8 6.6 Enterprise and Data Storage (Including Drives) 1,071.5 7.1 1,053.1 7.5 1,067.2 8.2 Other Hardware 3,100.3 20.4 3,042.6 21.8 2,950.5 22.7 Total Hardware 11,941.9 78.7 10,987.6 78.6 10,289.4 79.1 Software 2,540.1 16.7 2,389.3 17.1 2,152.3 16.6 Services (2) 611.3 4.0 575.1 4.1 467.7 3.6 Other (3) 98.2 0.6 29.9 0.2 79.3 0.7 Total Net sales $ 15,191.5 100.0 % $ 13,981.9 100.0 % $ 12,988.7 100.0 % (1) Amounts have been reclassified for changes in individual product classifications to conform to the presentation for the year ended December 31, 2017 . (2) Certain software and services revenue are recorded on a net basis for accounting purposes, so the category percentage of net revenues is not representative of the category percentage of gross profits. (3) Includes items such as delivery charges to customers and certain commission revenue.

Supplemental Guarantor Inform44

Supplemental Guarantor Information (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Guarantor Information [Abstract]
Schedule of Condensed Balance Sheet	Condensed Consolidating Balance Sheet December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Assets Current assets: Cash and cash equivalents $ — $ 113.7 $ — $ 32.4 $ — $ (1.9 ) $ 144.2 Accounts receivable, net — — 2,007.7 312.8 — — 2,320.5 Merchandise inventory — — 375.7 73.8 — — 449.5 Miscellaneous receivables — 103.9 205.0 27.6 — — 336.5 Prepaid expenses and other — 18.0 61.4 48.0 — — 127.4 Total current assets — 235.6 2,649.8 494.6 — (1.9 ) 3,378.1 Property and equipment, net — 95.0 43.5 22.6 — — 161.1 Goodwill — 751.8 1,439.0 288.8 — — 2,479.6 Other intangible assets, net — 280.1 424.5 192.4 — — 897.0 Other assets 1.7 30.7 217.3 2.6 — (211.5 ) 40.8 Investment in and advances to subsidiaries 981.2 3,063.5 — — — (4,044.7 ) — Total Assets $ 982.9 $ 4,456.7 $ 4,774.1 $ 1,001.0 $ — $ (4,258.1 ) $ 6,956.6 Liabilities and Stockholders’ Equity Current liabilities: Accounts payable-trade $ — $ 42.5 $ 1,112.1 $ 165.0 $ — $ (1.9 ) $ 1,317.7 Accounts payable-inventory financing — 1.0 480.9 16.1 — — 498.0 Current maturities of long-term debt — 14.9 3.8 6.8 — — 25.5 Deferred revenue — — 104.5 89.5 — — 194.0 Accrued expenses — 173.3 222.3 83.8 — — 479.4 Total current liabilities — 231.7 1,923.6 361.2 — (1.9 ) 2,514.6 Long-term liabilities: Debt — 3,134.2 8.3 67.5 — — 3,210.0 Deferred income taxes — 66.5 100.1 31.4 — (1.7 ) 196.3 Other liabilities — 43.1 4.6 214.9 — (209.8 ) 52.8 Total long-term liabilities — 3,243.8 113.0 313.8 — (211.5 ) 3,459.1 Total stockholders’ equity 982.9 981.2 2,737.5 326.0 — (4,044.7 ) 982.9 Total Liabilities and Stockholders’ Equity $ 982.9 $ 4,456.7 $ 4,774.1 $ 1,001.0 $ — $ (4,258.1 ) $ 6,956.6 Condensed Consolidating Balance Sheet December 31, 2016 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Assets Current assets: Cash and cash equivalents $ — $ 222.7 $ 3.1 $ 37.9 $ — $ — $ 263.7 Accounts receivable, net — — 1,904.9 263.7 — — 2,168.6 Merchandise inventory — — 390.6 61.4 — — 452.0 Miscellaneous receivables — 92.6 130.1 12.2 — — 234.9 Prepaid expenses and other — 14.3 69.0 35.6 — — 118.9 Total current assets — 329.6 2,497.7 410.8 — — 3,238.1 Property and equipment, net — 105.6 49.3 8.8 — — 163.7 Goodwill — 751.8 1,439.0 264.2 — — 2,455.0 Other intangible assets, net — 291.5 565.1 199.0 — — 1,055.6 Other assets 3.2 19.4 248.2 1.5 — (236.3 ) 36.0 Investment in and advances to subsidiaries 1,042.3 3,026.5 — — — (4,068.8 ) — Total Assets $ 1,045.5 $ 4,524.4 $ 4,799.3 $ 884.3 $ — $ (4,305.1 ) $ 6,948.4 Liabilities and Stockholders’ Equity Current liabilities: Accounts payable-trade $ — $ 25.9 $ 895.3 $ 151.7 $ — $ — $ 1,072.9 Accounts payable-inventory financing — 1.2 559.5 19.7 — — 580.4 Current maturities of long-term debt — 14.9 3.6 — — — 18.5 Deferred revenue — — 100.8 71.8 — — 172.6 Accrued expenses — 173.9 214.8 47.7 — (0.1 ) 436.3 Total current liabilities — 215.9 1,774.0 290.9 — (0.1 ) 2,280.7 Long-term liabilities: Debt — 3,136.3 12.1 67.5 — — 3,215.9 Deferred income taxes — 99.1 205.4 67.9 — (3.2 ) 369.2 Other liabilities — 30.8 3.6 235.7 — (233.0 ) 37.1 Total long-term liabilities — 3,266.2 221.1 371.1 — (236.2 ) 3,622.2 Total stockholders’ equity 1,045.5 1,042.3 2,804.2 222.3 — (4,068.8 ) 1,045.5 Total Liabilities and Stockholders’ Equity $ 1,045.5 $ 4,524.4 $ 4,799.3 $ 884.3 $ — $ (4,305.1 ) $ 6,948.4
Schedule of Condensed Income Statement	Consolidating Statement of Operations Year Ended December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Subsidiaries Co-Issuer Consolidating Adjustments Consolidated Net sales $ — $ — $ 13,631.0 $ 1,560.5 $ — $ — $ 15,191.5 Cost of sales — — 11,436.1 1,305.5 — — 12,741.6 Gross profit — — 2,194.9 255.0 — — 2,449.9 Selling and administrative expenses — 127.2 1,093.1 189.8 — — 1,410.1 Advertising expense — — 166.4 7.3 — — 173.7 Income (loss) from operations — (127.2 ) 935.4 57.9 — — 866.1 Interest (expense) income, net — (148.3 ) 4.1 (6.3 ) — — (150.5 ) Net loss on extinguishments of long-term debt — (57.4 ) — — — — (57.4 ) Other income (expense), net — (0.1 ) 0.7 1.5 — — 2.1 Income (loss) before income taxes — (333.0 ) 940.2 53.1 — — 660.3 Income tax (expense) benefit (0.9 ) 149.9 (269.7 ) (16.6 ) — — (137.3 ) Income (loss) before equity in earnings of subsidiaries (0.9 ) (183.1 ) 670.5 36.5 — — 523.0 Equity in earnings of subsidiaries 523.9 707.0 — — — (1,230.9 ) — Net income $ 523.0 $ 523.9 $ 670.5 $ 36.5 $ — $ (1,230.9 ) $ 523.0 Consolidating Statement of Operations Year Ended December 31, 2016 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Net sales $ — $ — $ 12,619.3 $ 1,362.6 $ — $ — $ 13,981.9 Cost of sales — — 10,514.4 1,140.3 — — 11,654.7 Gross profit — — 2,104.9 222.3 — — 2,327.2 Selling and administrative expenses — 114.8 1,057.4 172.9 — — 1,345.1 Advertising expense — — 157.2 5.7 — — 162.9 Income (loss) from operations — (114.8 ) 890.3 43.7 — — 819.2 Interest (expense) income, net — (145.8 ) 6.7 (7.4 ) — — (146.5 ) Net loss on extinguishments of long-term debt — (2.1 ) — — — — (2.1 ) Other income, net — 0.2 1.0 0.6 — — 1.8 Income (loss) before income taxes — (262.5 ) 898.0 36.9 — — 672.4 Income tax (expense) benefit — 79.9 (319.9 ) (8.0 ) — — (248.0 ) Income (loss) before equity in earnings of subsidiaries — (182.6 ) 578.1 28.9 — — 424.4 Equity in earnings of subsidiaries 424.4 607.0 — — — (1,031.4 ) — Net income $ 424.4 $ 424.4 $ 578.1 $ 28.9 $ — $ (1,031.4 ) $ 424.4 Consolidating Statement of Operations Year Ended December 31, 2015 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Net sales $ — $ — $ 12,151.2 $ 837.5 $ — $ — $ 12,988.7 Cost of sales — — 10,158.6 714.3 — — 10,872.9 Gross profit — — 1,992.6 123.2 — — 2,115.8 Selling and administrative expenses — 114.5 1,020.9 90.6 — — 1,226.0 Advertising expense — — 143.2 4.6 — — 147.8 Income (loss) from operations — (114.5 ) 828.5 28.0 — — 742.0 Interest (expense) income, net — (158.3 ) 2.3 (3.5 ) — — (159.5 ) Net loss on extinguishments of long-term debt — (24.3 ) — — — — (24.3 ) Management fee — 4.2 — (4.2 ) — — — Gain on remeasurement of equity investment — — — 98.1 — — 98.1 Other (expense) income, net — (11.1 ) 1.6 0.2 — — (9.3 ) Income (loss) before income taxes — (304.0 ) 832.4 118.6 — — 647.0 Income tax (expense) benefit — 103.3 (307.2 ) (40.0 ) — — (243.9 ) Income (loss) before equity in earnings of subsidiaries — (200.7 ) 525.2 78.6 — — 403.1 Equity in earnings of subsidiaries 403.1 603.8 — — — (1,006.9 ) — Net income $ 403.1 $ 403.1 $ 525.2 $ 78.6 $ — $ (1,006.9 ) $ 403.1
Schedule of Condensed Comprehensive Income (Loss)	Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Subsidiaries Co-Issuer Consolidating Adjustments Consolidated Comprehensive income $ 566.7 $ 567.6 $ 670.5 $ 80.0 $ — $ (1,318.1 ) $ 566.7 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2016 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Comprehensive income (loss) $ 345.9 $ 345.9 $ 578.1 $ (49.6 ) $ — $ (874.4 ) $ 345.9 Condensed Consolidating Statement of Comprehensive Income Year Ended December 31, 2015 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Comprehensive income $ 358.6 $ 358.6 $ 525.2 $ 34.1 $ — $ (917.9 ) $ 358.6
Schedule of Condensed Cash Flow Statement	Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2017 (in millions) Parent Guarantor Subsidiary Issuer Guarantor Subsidiaries Non-Guarantor Co-Issuer Consolidating Adjustments Consolidated Net cash provided by (used in) operating activities $ 0.6 $ (71.1 ) $ 788.5 $ 52.3 $ — $ 7.4 $ 777.7 Cash flows used in investing activities: Capital expenditures — (55.2 ) (6.3 ) (19.6 ) — — (81.1 ) Net cash used in investing activities — (55.2 ) (6.3 ) (19.6 ) — — (81.1 ) Cash flows (used in) provided by: financing activities: Proceeds from borrowings under revolving credit facility — 1,501.5 — 59.2 — — 1,560.7 Repayments of borrowings under revolving credit facility — (1,501.5 ) — (59.2 ) — — (1,560.7 ) Repayments of long-term debt — (14.9 ) — — — — (14.9 ) Proceeds from issuance of long-term debt — 2,083.0 — — — — 2,083.0 Payments to extinguish long-term debt — (2,121.3 ) — — — — (2,121.3 ) Net change in other long-term obligation — — (3.8 ) — — — (3.8 ) Payment of debt financing costs — (9.6 ) — — — — (9.6 ) Net change in accounts payable-inventory financing — (0.2 ) (78.4 ) (5.4 ) — — (84.0 ) Effective portion of interest rate cap agreements — 0.4 — — — — 0.4 Proceeds from stock option exercises — 13.0 — — — — 13.0 Proceeds from Coworker stock purchase plan — 10.3 — — — — 10.3 Repurchases of common stock (534.0 ) — — — — — (534.0 ) Payment of incentive compensation plan withholding taxes (49.6 ) — — — — — (49.6 ) Dividends (106.9 ) — — — — — (106.9 ) Principal payments under capital lease obligations — — (0.2 ) (1.1 ) — — (1.3 ) Repayment of intercompany loan — — 34.3 (34.3 ) — — — Distributions and advances from (to) affiliates 689.9 56.6 (737.2 ) — — (9.3 ) — Net cash (used in) provided by financing activities (0.6 ) 17.3 (785.3 ) (40.8 ) — (9.3 ) (818.7 ) Effect of exchange rate changes on cash and cash equivalents — — — 2.6 — — 2.6 Net decrease in cash and cash equivalents — (109.0 ) (3.1 ) (5.5 ) — (1.9 ) (119.5 ) Cash and cash equivalents – beginning of period — 222.7 3.1 37.9 — — 263.7 Cash and cash equivalents – end of period $ — $ 113.7 $ — $ 32.4 $ — $ (1.9 ) $ 144.2 Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2016 (in millions) Parent Subsidiary Guarantor Non-Guarantor Co-Issuer Consolidating Consolidated Net cash provided by (used in) operating activities $ — $ (158.5 ) $ 695.5 $ 56.1 $ — $ 10.9 $ 604.0 Cash flows used in investing activities: Capital expenditures — (50.9 ) (7.6 ) (5.0 ) — — (63.5 ) Premium payments on interest rate cap agreements — (2.4 ) — — — — (2.4 ) Net cash used in investing activities — (53.3 ) (7.6 ) (5.0 ) — — (65.9 ) Cash flows (used in) provided by financing activities: Proceeds from borrowings under revolving credit facility — 329.6 — 9.2 — — 338.8 Repayments of borrowings under revolving credit facility — (329.6 ) — (9.2 ) — — (338.8 ) Repayments of long-term debt — (15.2 ) — (5.4 ) — — (20.6 ) Proceeds from issuance of long-term debt — 1,483.0 — — — — 1,483.0 Payments to extinguish long-term debt — (1,490.4 ) — — — — (1,490.4 ) Net change in other long-term obligation — — 15.7 — — — 15.7 Payment of debt financing costs — (4.5 ) — (1.4 ) — — (5.9 ) Net change in accounts payable - inventory financing — 1.5 131.0 11.1 — — 143.6 Proceeds from stock option exercises — 7.4 — — — — 7.4 Proceeds from Coworker Stock Purchase Plan — 9.3 — — — — 9.3 Repurchases of common stock (367.4 ) — — — — — (367.4 ) Dividends (78.7 ) — — — — — (78.7 ) Principal payments under capital lease obligations — — 1.0 (1.6 ) — — (0.6 ) Repayment of intercompany loan — — 40.4 (40.4 ) — — — Distributions and advances from (to) affiliates 446.1 398.3 (872.9 ) — — 28.5 — Net cash (used in) provided by financing activities — 389.4 (684.8 ) (37.7 ) — 28.5 (304.6 ) Effect of exchange rate changes on cash and cash equivalents — — — (7.4 ) — — (7.4 ) Net increase in cash and cash equivalents — 177.6 3.1 6.0 — 39.4 226.1 Cash and cash equivalents—beginning of period — 45.1 — 31.9 — (39.4 ) 37.6 Cash and cash equivalents—end of period $ — $ 222.7 $ 3.1 $ 37.9 $ — $ — $ 263.7 Condensed Consolidating Statement of Cash Flows Year Ended December 31, 2015 (in millions) Parent Subsidiary Guarantor Non-Guarantor Co-Issuer Consolidating Consolidated Net cash provided (used in) by operating activities $ 0.5 $ (18.1 ) $ 350.0 $ 27.9 $ — $ (82.8 ) $ 277.5 Cash flows from investing activities: Capital expenditures — (75.4 ) (11.6 ) (3.1 ) — — (90.1 ) Premium payments on interest rate cap agreements — (0.5 ) — — — — (0.5 ) Acquisition of business, net of cash acquired — — — (263.8 ) — — (263.8 ) Net cash used in investing activities — (75.9 ) (11.6 ) (266.9 ) — — (354.4 ) Cash flows from financing activities: Proceeds from borrowings under revolving credit facility — 314.5 — — — — 314.5 Repayments of borrowings under revolving credit facility — (314.5 ) — — — — (314.5 ) Repayments of long-term debt — (15.4 ) — (17.4 ) — — (32.8 ) Proceeds from issuance of long-term debt — 525.0 — — — — 525.0 Payments to extinguish long-term debt — (525.3 ) — — — — (525.3 ) Payment of debt financing costs — (6.8 ) — — — — (6.8 ) Net change in accounts payable-inventory financing — — 96.1 (0.2 ) — — 95.9 Proceeds from stock option exercises — 2.4 — — — — 2.4 Proceeds from Coworker stock purchase plan — 8.7 — — — — 8.7 Repurchases of common stock (241.3 ) — — — — — (241.3 ) Payment of incentive compensation plan withholding taxes — 0.6 — — — — 0.6 Dividends (52.9 ) — — — — — (52.9 ) Distributions and advances from (to) affiliates 293.7 (196.5 ) (434.5 ) 267.4 — 69.9 — Net cash (used in) provided by financing activities (0.5 ) (207.3 ) (338.4 ) 249.8 — 69.9 (226.5 ) Effect of exchange rate changes on cash and cash equivalents — — — (3.5 ) — — (3.5 ) Net (decrease) increase in cash and cash equivalents — (301.3 ) — 7.3 — (12.9 ) (306.9 ) Cash and cash equivalents – beginning of period — 346.4 — 24.6 — (26.5 ) 344.5 Cash and cash equivalents – end of period $ — $ 45.1 $ — $ 31.9 $ — $ (39.4 ) $ 37.6

Selected Quarterly Financial 45

Selected Quarterly Financial Results (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Year Ended December 31, 2017 (1) (in millions, except per-share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Net Sales: Corporate $ 1,476.3 $ 1,630.7 $ 1,598.5 $ 1,641.4 Small Business 298.7 321.5 311.5 314.8 Public: Government 386.9 543.9 606.7 630.0 Education 397.1 712.9 700.7 400.8 Healthcare 392.5 417.3 425.5 423.3 Total Public 1,176.5 1,674.1 1,732.9 1,454.1 Other 373.2 368.1 391.0 428.3 Net sales $ 3,324.7 $ 3,994.4 $ 4,033.9 $ 3,838.6 Gross profit $ 552.6 $ 641.1 $ 642.0 $ 614.4 Income from operations 169.8 231.1 243.7 221.6 Net income (2) 57.6 141.0 129.2 195.2 Basic (3) 0.36 0.90 0.84 1.28 Diluted (3) 0.35 0.89 0.83 1.26 Cash dividends declared per common share $ 0.1600 $ 0.1600 $ 0.1600 $ 0.2100 Year Ended December 31, 2016 (1) (in millions, except per-share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter Net Sales: Corporate (4) $ 1,414.9 $ 1,490.8 $ 1,466.4 $ 1,517.7 Small Business (4) 277.4 288.4 282.5 291.8 Public: Government 339.9 456.6 537.5 529.6 Education 341.0 640.0 671.4 365.9 Healthcare 388.5 450.4 431.7 436.8 Total Public 1,069.4 1,547.0 1,640.6 1,332.3 Other 355.0 338.4 318.7 350.5 Net sales $ 3,116.7 $ 3,664.6 $ 3,708.2 $ 3,492.4 Gross profit $ 524.5 $ 610.5 $ 614.3 $ 577.9 Income from operations 161.0 223.5 237.5 197.2 Net income 77.8 117.5 125.9 103.2 Basic (3) 0.47 0.71 0.78 0.64 Diluted (3) 0.46 0.70 0.76 0.63 Cash dividends declared per common share $ 0.1075 $ 0.1075 $ 0.1075 $ 0.1600 (1) Sum of quarters may not agree to reported yearly totals due to rounding. (2) The fourth quarter of 2017 includes the benefit of the Tax Cuts and Jobs Act enacted during 2017. For information regarding the Tax Cuts and Jobs Act, see Note 11 (Income Taxes) . (3) Basic and diluted net income per share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted net income per share. (4) Amounts have been recast to present Small Business as its own operating and reportable segment.

Description of Business and S46

Description of Business and Summary of Significant Accounting Policies - Description of Business (Details) - subsidiary	Dec. 31, 2017	Aug. 31, 2015
Business Acquisition [Line Items]
Number of owned subsidiaries	2
Kelway TopCo Limited
Business Acquisition [Line Items]
Percent of outstanding common stock purchased		65.00%
Non-controlling interest held		35.00%
Total percentage owned, after acquisition		100.00%

Description of Business and S47

Description of Business and Summary of Significant Accounting Policies - Property Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Asset retirement liability (less than)	$ 2	$ 1
Minimum | Machinery and equipment
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Minimum | Building and leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Minimum | Computer and data processing equipment
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	3 years
Minimum | Computer software
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	3 years
Minimum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Maximum | Machinery and equipment
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	10 years
Maximum | Building and leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	25 years
Maximum | Computer and data processing equipment
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Maximum | Computer software
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Maximum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	10 years

Description of Business and S48

Description of Business and Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment test, income approach weight	75.00%
Goodwill impairment test, market approach weight	25.00%
Years forecasted in goodwill impairment income approach	5 years
Minimum
Finite-Lived Intangible Assets [Line Items]
Long-term consolidated annual growth rate	2.00%
Minimum | Customer relationships and contracts
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	3 years
Minimum | Internally developed software
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	3 years
Minimum | Other
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Long-term consolidated annual growth rate	3.50%
Maximum | Customer relationships and contracts
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	14 years
Maximum | Trade name
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	20 years
Maximum | Internally developed software
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	5 years
Maximum | Other
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of intangible assets	10 years

Description of Business and S49

Description of Business and Summary of Significant Accounting Policies - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stockholders' equity	$ 982.9	$ 1,045.5	$ 1,095.9	$ 936.5
Foreign currency translation
Stockholders' equity	(96.1)	(139.6)	(61.1)
Unrealized gain from hedge accounting
Stockholders' equity	0.2	0	0
Accumulated Other Comprehensive Loss
Stockholders' equity	$ (95.9)	$ (139.6)	$ (61.1)	$ (16.6)

Recent Accounting Pronounceme50

Recent Accounting Pronouncements - Adoption of ASU, Expected Impact (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement Related Disclosures [Abstract]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Gross profit	614.4	642	641.1	552.6	577.9	614.3	610.5	524.5	$ 2,449.9	$ 2,327.2	2,115.8
Gross profit margin									16.10%	16.60%
Income from operations	221.6	243.7	231.1	169.8	197.2	237.5	223.5	161	$ 866.1	$ 819.2	742
Income tax expense									(137.3)	(248)	(243.9)
Net income	$ 195.2	$ 129.2	$ 141	$ 57.6	$ 103.2	$ 125.9	$ 117.5	$ 77.8	$ 523	$ 424.4	$ 403.1
Net income per common share:
Earnings per share, basic (in dollars per share)	$ 1.28	$ 0.84	$ 0.90	$ 0.36	$ 0.64	$ 0.78	$ 0.71	$ 0.47	$ 3.37	$ 2.59	$ 2.37
Earnings per share, diluted (in dollars per share)	$ 1.26	$ 0.83	$ 0.89	$ 0.35	$ 0.63	$ 0.76	$ 0.70	$ 0.46	$ 3.31	$ 2.56	$ 2.35
Balance Sheet Related Disclosures [Abstract]
Accounts receivable, net	$ 2,320.5				$ 2,168.6				$ 2,320.5	$ 2,168.6
Merchandise inventory	449.5				452				449.5	452
Miscellaneous receivables	336.5				234.9				336.5	234.9
Prepaid expenses and other	127.4				118.9				127.4	118.9
Total current assets	3,378.1				3,238.1				3,378.1	3,238.1
Other assets	40.8				36				40.8	36
Total assets	6,956.6				6,948.4				6,956.6	6,948.4
Deferred revenue	194				172.6				194	172.6
Income tax payable	15.1				2.6				15.1	2.6
Other accrued expenses	180.2				147.2				180.2	147.2
Total current liabilities	2,514.6				2,280.7				2,514.6	2,280.7
Total liabilities	5,973.7				5,902.9				5,973.7	5,902.9
Total stockholders’ equity	982.9				1,045.5				982.9	1,045.5	$ 1,095.9	$ 936.5
Pro Forma
Income Statement Related Disclosures [Abstract]
Net sales									14,832.9	13,672.7
Gross profit									$ 2,450.2	$ 2,328.3
Gross profit margin									16.50%	17.00%
Income from operations									$ 866.5	$ 820
Income tax expense									(137.6)	(248.1)
Net income									$ 523.1	$ 425.1
Net income per common share:
Earnings per share, basic (in dollars per share)									$ 3.37	$ 2.60
Earnings per share, diluted (in dollars per share)									$ 3.31	$ 2.56
Balance Sheet Related Disclosures [Abstract]
Accounts receivable, net	2,329.3				2,168.9				$ 2,329.3	$ 2,168.9
Merchandise inventory	411.5				423.9				411.5	423.9
Miscellaneous receivables	343				237.5				343	237.5
Prepaid expenses and other	168.3				154.2				168.3	154.2
Total current assets	3,396.3				3,248.2				3,396.3	3,248.2
Other assets	32.7				35.9				32.7	35.9
Total assets	6,966.7				6,958.4				6,966.7	6,958.4
Deferred revenue	158.8				143.5				158.8	143.5
Income tax payable	16.2				3.3				16.2	3.3
Other accrued expenses	221.8				183.2				221.8	183.2
Total current liabilities	2,522.1				2,288.3				2,522.1	2,288.3
Total liabilities	5,981.1				5,910.5				5,981.1	5,910.5
Total stockholders’ equity	985.6				1,047.9				985.6	1,047.9
Difference between Revenue Guidance in Effect before and after Topic 606 | Pro Forma | Accounting Standards Update 2014-09
Income Statement Related Disclosures [Abstract]
Net sales									(358.6)	(309.2)
Gross profit									$ 0.3	$ 1.1
Gross profit margin									0.40%	0.40%
Income from operations									$ 0.4	$ 0.8
Income tax expense									(0.3)	(0.1)
Net income									$ 0.1	$ 0.7
Net income per common share:
Earnings per share, basic (in dollars per share)									$ 0	$ 0.01
Earnings per share, diluted (in dollars per share)									$ 0	$ 0
Balance Sheet Related Disclosures [Abstract]
Accounts receivable, net	8.8				0.3				$ 8.8	$ 0.3
Merchandise inventory	(38)				(28.1)				(38)	(28.1)
Miscellaneous receivables	6.5				2.6				6.5	2.6
Prepaid expenses and other	40.9				35.3				40.9	35.3
Total current assets	18.2				10.1				18.2	10.1
Other assets	(8.1)				(0.1)				(8.1)	(0.1)
Total assets	10.1				10				10.1	10
Deferred revenue	(35.2)				(29.1)				(35.2)	(29.1)
Income tax payable	1.1				0.7				1.1	0.7
Other accrued expenses	41.6				36				41.6	36
Total current liabilities	7.5				7.6				7.5	7.6
Total liabilities	7.5				7.6				7.5	7.6
Total stockholders’ equity	$ 2.7				$ 2.4				$ 2.7	$ 2.4

Acquisition - Narrative (Detail

Acquisition - Narrative (Details) - CDW UK	Aug. 01, 2015
Business Acquisition [Line Items]
Percent of outstanding common stock purchased	65.00%
Non-controlling interest held	35.00%
Total percentage owned, after acquisition	100.00%

Acquisition - Fair Value of Con

Acquisition - Fair Value of Consideration Transferred (Details) - USD ($) $ in Millions	Aug. 01, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Gain on remeasurement of equity investment		$ 0	$ 0	$ 98.1
CDW UK
Business Acquisition [Line Items]
Cash	$ 291.6
Fair value of CDW common stock	33.2
Fair value of previously held equity investment on the date of acquisition	174.9
Total consideration	$ 499.7
Shares issued during acquisition	1,634,809
Restriction period for common shares issued	3 years
Options issued by one of the sellers to certain coworkers over shares of the seller's common stock received as part of consideration from acquisition	608,706
Fair value of options issued by one of the sellers to certain coworkers over shares of the seller's common stock received as part of consideration from acquisition	$ 22
Weighted-average service period of options issued by one of the sellers to certain coworkers over shares of the seller's common stock received as part of consideration from acquisition	3 years 2 months 12 days
Non-controlling interest held	35.00%
Gain on remeasurement of equity investment	$ 98

Acquisition - Pro Forma Informa

Acquisition - Pro Forma Information (Details) - CDW UK - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Aug. 01, 2015
Business Acquisition [Line Items]
Net sales	$ 13,507.6
Net income	$ 363.7
Non-controlling interest held		35.00%

Miscellaneous Receivables (Deta

Miscellaneous Receivables (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Vendor partner receivables	$ 279.2	$ 186.6
Other	57.3	48.3
Total	$ 336.5	$ 234.9

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Building and leasehold improvements	$ 123	$ 120.4
Computer and data processing equipment	116.4	101.7
Machinery and equipment	45.6	43.2
Land	27.7	27.7
Furnitures and fixtures	22.7	23.8
Construction in progress	17.9	20.4
Computer software	9.6	10.8
Property and equipment, gross	362.9	348
Less: accumulated depreciation	(201.8)	(184.3)
Property and equipment, net	$ 161.1	$ 163.7

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property and equipment, disposals recorded	$ 23	$ 50	$ 17
Pre-tax loss for disposed assets (less than)	(1)	(1)	(1)
Depreciation expense	$ 40	$ 38	$ 29

Goodwill and Other Intangible57

Goodwill and Other Intangible Assets - Schedule of Goodwill by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Beginning balance	$ 2,455	$ 2,500.4	$ 2,217.6
Foreign currency translation	24.6	(45.4)	(22.4)
Acquisition			305.2
CDW Advanced Services Allocation		0
Ending balance	2,479.6	2,455	2,500.4
Corporate
Goodwill [Roll Forward]
Beginning balance	1,074.1	1,045.9	1,045.9
Foreign currency translation	0	0	0
Acquisition			0
CDW Advanced Services Allocation		28.2
Ending balance	1,074.1	1,074.1	1,045.9
Accumulated impairment losses		(1,571.4)
Small Business
Goodwill [Roll Forward]
Beginning balance	185.9	185.9	185.9
Foreign currency translation	0	0	0
Acquisition			0
CDW Advanced Services Allocation		0
Ending balance	185.9	185.9	185.9
Public
Goodwill [Roll Forward]
Beginning balance	929.6	911.3	911.3
Foreign currency translation	0	0	0
Acquisition			0
CDW Advanced Services Allocation		18.3
Ending balance	929.6	929.6	911.3
Accumulated impairment losses		(354.1)
Other
Goodwill [Roll Forward]
Beginning balance	265.4	357.3	74.5
Foreign currency translation	24.6	(45.4)	(22.4)
Acquisition			305.2
CDW Advanced Services Allocation		(46.5)
Ending balance	$ 290	265.4	$ 357.3
Accumulated impairment losses		$ (28.3)

Goodwill and Other Intangible58

Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 01, 2017	Jan. 01, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill impairment loss	$ 0	$ 0
Amortization expense	221	216	$ 199
Internally developed software
Acquired Finite-Lived Intangible Assets [Line Items]
Disposal of fully amortized definite-lived intangible assets	$ 24	$ 29
Corporate
Acquired Finite-Lived Intangible Assets [Line Items]
Fair values of reporting units, in excess of carrying value (as a percent)					227.00%
Small Business
Acquired Finite-Lived Intangible Assets [Line Items]
Fair values of reporting units, in excess of carrying value (as a percent)					308.00%
Public
Acquired Finite-Lived Intangible Assets [Line Items]
Fair values of reporting units, in excess of carrying value (as a percent)				179.00%
CANADA
Acquired Finite-Lived Intangible Assets [Line Items]
Fair values of reporting units, in excess of carrying value (as a percent)				153.00%

Goodwill and Other Intangible59

Goodwill and Other Intangible Assets - Intangible Assets by Asset Type (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,694.5	$ 2,655.3
Accumulated Amortization	(1,797.5)	(1,599.7)
Net Carrying Amount	897	1,055.6
Customer relationships and contracts
Intangible Assets [Line Items]
Gross Carrying Amount	2,106.8	2,084.6
Accumulated Amortization	(1,490.8)	(1,322.7)
Net Carrying Amount	616	761.9
Trade name
Intangible Assets [Line Items]
Gross Carrying Amount	422.2	422.1
Accumulated Amortization	(216.3)	(195.2)
Net Carrying Amount	205.9	226.9
Internally developed software
Intangible Assets [Line Items]
Gross Carrying Amount	162.6	142.6
Accumulated Amortization	(89.6)	(77.7)
Net Carrying Amount	73	64.9
Other
Intangible Assets [Line Items]
Gross Carrying Amount	2.9	6
Accumulated Amortization	(0.8)	(4.1)
Net Carrying Amount	$ 2.1	$ 1.9

Goodwill and Other Intangible60

Goodwill and Other Intangible Assets - Amortization of Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 219.8
2,019	201.4
2,020	167.6
2,021	72.3
2,022	38.4
Thereafter	197.5
Total future amortization expense	$ 897	$ 1,055.6

Inventory Financing Agreement61

Inventory Financing Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Inventory Financing Agreements [Line Items]
Accounts payable-inventory financing	$ 498	$ 580.4
Accounts Payable, Inventory Financing
Inventory Financing Agreements [Line Items]
Revolving Loan financing agreement	480.9	558.3
Other inventory financing agreements	17.1	22.1
Accounts payable-inventory financing	498	580.4
Accounts Payable, Inventory Financing Collateralized
Inventory Financing Agreements [Line Items]
Other inventory financing agreements	$ 1	$ 3

Lease Commitments - Narrative (

Lease Commitments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases [Abstract]
Rent expense under lease arrangements	$ 29	$ 27	$ 25

Lease Commitments - Operating L

Lease Commitments - Operating Leases (Details) $ in Millions	Dec. 31, 2017USD ($)
Leases [Abstract]
2,018	$ 22.1
2,019	21.8
2,020	21
2,021	14.5
2,022	9
Thereafter	43.4
Total future minimum lease payments	$ 131.8

Financial Instruments - Narrati

Financial Instruments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cap agreement effective 1/1/17-12/31/18
Derivative [Line Items]
Interest rate cap, cap rate	1.50%
Notional amount	$ 1,400
Interest rate cap, fair value	5	$ 5
Interest Rate Contract
Derivative [Line Items]
Amount to be reclassified from AOCL to interest expense	5
Derivative
Derivative [Line Items]
Interest gain (loss) reclassified to earnings	$ 1	$ 3

Long-Term Debt - Debt Balances

Long-Term Debt - Debt Balances and Interest Rates (Details) £ in Millions, $ in Millions	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)	Mar. 02, 2017USD ($)	Dec. 31, 2016USD ($)	Aug. 01, 2016USD ($)	Aug. 01, 2016GBP (£)
Debt Instrument [Line Items]
Long-term debt	$ 3,255.9			$ 3,267.8
Long-term debt, current maturities, gross	(25.5)			(18.5)
Long-term debt, excluding current maturities, gross	3,230.4			3,249.3
Deferred finance costs, net	(20.4)			(33.4)
Deferred finance costs, current, net	0			0
Deferred finance costs, noncurrent, net	(20.4)			(33.4)
Long-term debt, net of deferred financing costs	3,235.5			3,234.4
Current maturities of long-term debt, net of deferred financing costs	(25.5)			(18.5)
Long-term debt, excluding current maturities, net of deferred financing costs	$ 3,210			$ 3,215.9
Senior secured asset-based revolving credit facility
Debt Instrument [Line Items]
Interest rate in effect	0.00%	0.00%		0.00%
Long-term debt	$ 0			$ 0
Deferred finance costs, net	0			0
Long-term debt, net of deferred financing costs	$ 0			$ 0
CDW UK revolving credit facility
Debt Instrument [Line Items]
Interest rate in effect	0.00%	0.00%		0.00%
Long-term debt	$ 0	£ 0		$ 0
Deferred finance costs, net	0			0
Long-term debt, net of deferred financing costs	$ 0			$ 0
Senior secured term loan facility
Debt Instrument [Line Items]
Interest rate in effect	3.70%	3.70%		3.30%
Long-term debt	$ 1,468			$ 1,483
Deferred finance costs, net	(2)			(14.9)
Long-term debt, net of deferred financing costs	$ 1,466			$ 1,468.1
CDW UK term loan
Debt Instrument [Line Items]
Interest rate in effect	1.92%	1.92%		1.80%
Long-term debt	$ 75.7			$ 69.1	$ 76	£ 56
Deferred finance costs, net	(1.4)			(1.6)
Long-term debt, net of deferred financing costs	$ 74.3			$ 67.5
Senior notes due 2022
Debt Instrument [Line Items]
Interest rate in effect				6.00%
Long-term debt			$ 600	$ 600
Deferred finance costs, net				(5.6)
Long-term debt, net of deferred financing costs				$ 594.4
Senior notes due 2023
Debt Instrument [Line Items]
Interest rate in effect	5.00%	5.00%		5.00%
Long-term debt	$ 525			$ 525
Deferred finance costs, net	(4.5)			(5.3)
Long-term debt, net of deferred financing costs	$ 520.5			$ 519.7
Senior notes due 2024
Debt Instrument [Line Items]
Interest rate in effect	5.50%	5.50%		5.50%
Long-term debt	$ 575			$ 575
Deferred finance costs, net	(5.2)			(6)
Long-term debt, net of deferred financing costs	$ 569.8			569
Senior notes due 2025
Debt Instrument [Line Items]
Interest rate in effect	5.00%	5.00%
Long-term debt	$ 600		$ 600
Deferred finance costs, net	(7.3)
Long-term debt, net of deferred financing costs	592.7
Other long-term obligations
Debt Instrument [Line Items]
Long-term debt	12.2			15.7
Deferred finance costs, net	0			0
Long-term debt, net of deferred financing costs	$ 12.2			$ 15.7

Long-Term Debt - Revolving Loan

Long-Term Debt - Revolving Loan (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt, long-term and short-term		$ 3,255.9	$ 3,267.8
Net loss on extinguishments of long-term debt		(57.4)	(2.1)	$ (24.3)
Senior secured asset-based revolving credit facility
Debt Instrument [Line Items]
Debt, long-term and short-term		0	0
Additional borrowing capacity		996
Undrawn letters of credit		1
Borrowing base		1,600
Cash availability. minimum liquidity		$ 125
Cash availability, percentage of borrowing base		10.00%
Minimum liquidity, amount		$ 100
Basis spread on variable rate (as percent)		1.00%
Debt instrument term	5 years
Borrowing capacity of the Revolving Loan	$ 1,500		$ 1,250
Maximum aggregate increase	$ 300
Unused borrowing capacity	0.25%
Margin on borrowings, reduced interest rate from refinancing in bps	0.25%
Net loss on extinguishments of long-term debt		$ (1)
Capitalized fees as deferred financing costs		$ 4
Senior secured asset-based revolving credit facility | Minimum
Debt Instrument [Line Items]
Consolidated fixed charge coverage ratio		1
Senior secured asset-based revolving credit facility | Accounts Payable, Inventory Financing
Debt Instrument [Line Items]
Amount owed under Revolving loan financing agreement		$ 454
Senior secured asset-based revolving credit facility | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		0.50%
Senior secured asset-based revolving credit facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		1.25%
Senior secured asset-based revolving credit facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		1.75%
Senior secured asset-based revolving credit facility | ABR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		0.25%
Senior secured asset-based revolving credit facility | ABR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)		0.75%

Long-Term Debt - Term Loan (Det

Long-Term Debt - Term Loan (Details) £ in Millions, $ in Millions	Aug. 01, 2016USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2018GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017GBP (£)	Feb. 28, 2017	Aug. 01, 2016GBP (£)
Debt Instrument [Line Items]
Debt, long-term and short-term				$ 3,255.9	$ 3,267.8
Net loss on extinguishments of long-term debt				(57.4)	(2.1)	$ (24.3)
Senior secured term loan facility
Debt Instrument [Line Items]
Debt, long-term and short-term				1,468	$ 1,483
Debt issuance costs				$ 2
Quarterly amortization payment of original principal, Percent				0.25%			0.25%
Net loss on extinguishments of long-term debt				$ (14)
Write-off of unamortized deferred financing costs				5
Write-off of unamortized discount from prior term loan facility				9
Deferred financing fees incurred				$ 2
Interest rate in effect				3.70%	3.30%		3.70%
CDW UK term loan
Debt Instrument [Line Items]
Debt, long-term and short-term	$ 76			$ 75.7	$ 69.1				£ 56
Applicable margin				1.40%			1.40%
Debt instrument term	5 years
Capitalized fees as deferred financing costs				$ 1
Interest rate in effect				1.92%	1.80%		1.92%
CDW UK revolving credit facility
Debt Instrument [Line Items]
Debt, long-term and short-term				$ 0	$ 0		£ 0
Interest rate in effect				0.00%	0.00%		0.00%
Additional borrowing capacity				$ 68			£ 50
ABR | Senior secured term loan facility
Debt Instrument [Line Items]
Applicable margin				1.00%			1.00%
LIBOR | Senior secured term loan facility
Debt Instrument [Line Items]
Margin on borrowings, reduced interest rate from refinancing in bps								0.25%
Applicable margin				2.00%			2.00%
Scenario, Forecast | CDW UK term loan
Debt Instrument [Line Items]
Annual principal repayment installments		$ 7	£ 5

Long-Term Debt - Senior Notes (

Long-Term Debt - Senior Notes (Details) - USD ($) $ in Millions	Mar. 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt, long-term and short-term		$ 3,255.9	$ 3,267.8
Net loss on extinguishments of long-term debt		(57.4)	(2.1)	$ (24.3)
Deferred finance costs, net		$ 20.4	33.4
Senior notes due 2022
Debt Instrument [Line Items]
Stated interest rate		6.00%
Debt, long-term and short-term	$ 600		600
Redemption price, percentage	106.182%
Net loss on extinguishments of long-term debt		$ (43)
Redemption premium		37
Capitalized fees as deferred financing costs		$ 6
Deferred finance costs, net			5.6
Senior notes due 2023
Debt Instrument [Line Items]
Stated interest rate		5.00%
Debt, long-term and short-term		$ 525	525
Deferred finance costs, net		$ 4.5	5.3
Senior notes due 2024
Debt Instrument [Line Items]
Stated interest rate		5.50%
Debt, long-term and short-term		$ 575	575
Deferred finance costs, net		$ 5.2	$ 6
Senior notes due 2025
Debt Instrument [Line Items]
Stated interest rate		5.00%
Debt, long-term and short-term	$ 600	$ 600
Deferred finance costs, net		$ 7.3

Long-Term Debt - Debt Guarantor

Long-Term Debt - Debt Guarantors, Covenants and Restrictions (Details) £ in Millions, $ in Millions	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)
Senior secured term loan facility
Debt Instrument [Line Items]
Amount of restricted payment capacity under the loan	$ 1,153
Net leverage ratio	2.62	2.62
Senior secured term loan facility | Maximum
Debt Instrument [Line Items]
Net leverage ratio	3.25	3.25
CDW UK term loan
Debt Instrument [Line Items]
Amount of restricted payment capacity under the loan	$ 98	£ 73

Long-Term Debt - Long-Term Debt

Long-Term Debt - Long-Term Debt Maturities (Details) $ in Millions	Dec. 31, 2017USD ($)
Debt Disclosure [Abstract]
2,018	$ 25.5
2,019	25.7
2,020	25.9
2,021	70.3
2,022	14.9
Thereafter	3,093.6
Debt, total long-term and short-term	$ 3,255.9

Long-Term Debt - Fair Value of

Long-Term Debt - Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value	$ 3,255.9	$ 3,267.8
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	$ 3,366.5	$ 3,334.8

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Operating Loss Carryforwards [Line Items]
Income tax benefit from change in tax rate	$ 96
Income tax expense from transition tax for accumulated foreign earnings	20
Income tax expense from state impact	1
Deferred income tax expense related to basis difference in CDW UK	19
Deferred tax liability on unremitted CDW UK earnings	3
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	29
State tax credit carryforwards	28
Tax Cuts And Jobs Act Of 2017
Operating Loss Carryforwards [Line Items]
Valuation allowance	14
State tax credit carryforwards	$ 14

Income Taxes - Income Before In

Income Taxes - Income Before Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ 607.1	$ 635.5	$ 626.4
Foreign	53.2	36.9	20.6
Income before income taxes	$ 660.3	$ 672.4	$ 647

Income Taxes - Income Tax Expen

Income Taxes - Income Tax Expense by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 258.9	$ 295.7	$ 258.5
State	29.8	34.9	28.6
Foreign	21.3	16.8	10.1
Total current	310	347.4	297.2
Deferred:
Domestic	(168)	(90.5)	(48.5)
Foreign	(4.7)	(8.9)	(4.8)
Total deferred	(172.7)	(99.4)	(53.3)
Income tax expense	$ 137.3	$ 248	$ 243.9

Income Taxes - Effective Tax Ra

Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory federal income tax rate, amount	$ 231.1	$ 235.4	$ 226.4
State taxes, net of federal effect, amount	18.3	17.8	16.5
Equity based compensation, amount	(36.2)	(1.6)	0
Effect of rates different than statutory, amount	(6.3)	(4.5)	(1.9)
Foreign withholding tax, amount	1	0.8	3.3
Effect of U.K. tax rate change on deferred taxes, amount	0	(1.5)	(4)
Effect of US Tax Cuts and Jobs Act on Deferred Taxes, amount	(75.5)	0	0
Other, amount	4.9	1.6	3.6
Income tax expense	$ 137.3	$ 248	$ 243.9
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate, percent	35.00%	35.00%	35.00%
State taxes, net of federal effect, percent	2.80%	2.60%	2.60%
Equity based compensation, percent	(5.50%)	(0.20%)	0.00%
Effect of rates different than statutory, percent	(1.00%)	(0.70%)	(0.30%)
Foreign withholding tax, percent	0.20%	0.10%	0.50%
Effect of U.K. tax rate change on deferred taxes, percent	0.00%	(0.20%)	(0.60%)
Effect of US Tax Cuts and Jobs Act on Deferred Taxes, percent	(11.40%)	0.00%	0.00%
Other, percent	0.70%	0.30%	0.50%
Income tax expense, rate	20.80%	36.90%	37.70%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Equity compensation plans	$ 18.7	$ 29.2
Payroll and benefits	8	22.7
Deferred interest	6.8	13.9
Net operating loss and credit carryforwards, net	28.1	12.7
Rent	7.4	11
Accounts receivable	5.4	8.3
Other	8	6.2
Trade credits	1.5	0.6
Total deferred tax assets	83.9	104.6
Deferred tax liabilities:
Software and intangibles	194.5	337.4
Deferred income	18.6	58.3
International investments	19.2	31.3
Property and equipment	20.4	30.3
Other	12	15.3
Total deferred tax liabilities	264.7	472.6
Deferred tax asset valuation allowance	15.5	1.2
Net deferred tax liabilities	$ 196.3	$ 369.2

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2017	Nov. 30, 2015	Aug. 18, 2015	May 22, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 03, 2017
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired during the period (in shares)		1,000,000	2,300,000	2,000,000
Common stock repurchased and retired during the period					$ 534	$ 367.5	$ 241.3
Treasury stock acquired (in shares)	109,207
The Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired during the period (in shares)					8,893,993
Common stock repurchased and retired during the period					$ 534
Additional amount authorized under repurchase program								$ 750
Amount remaining under repurchase program	$ 858				$ 858

Equity-Based Compensation - Sum

Equity-Based Compensation - Summary of Equity-based Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-based compensation expense	$ 43.7	$ 39.2	$ 31.2
Income tax benefit	15.3	13.3	10.9
Equity-based compensation expense (net of tax)	28.4	$ 25.9	$ 20.3
Compensation cost not yet recognized	$ 32
Compensation cost not yet recognized, period for recognition	1 year 7 months 6 days

Equity-Based Compensation - 201

Equity-Based Compensation - 2013 Long-Term Incentive Plan (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2013
Restricted Stock Awards (RSAs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards granted in the period (in shares)	0	3,798,508
2013 Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	15,500,000
Number of share available for grant (in shares)	6,416,547

Equity-Based Compensation - Val

Equity-Based Compensation - Valuation Assumptions Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option contractual life	10 years
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Grant date fair value (in dollars per share)	$ 12.27	$ 8.55	$ 11.13
Volatility (as percent)	22.00%	25.00%	30.00%
Risk-free rate (as percent)	2.08%	1.47%	1.75%
Expected dividend yield (as percent)	1.09%	1.08%	0.72%
Expected term (in years)	6 years	6 years	6 years

Equity-Based Compensation - Sto

Equity-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning (in shares)	3,781,051
Granted (in shares)	1,213,299
Forfeitures/Expired (in shares)	(59,834)
Exercised (in shares)	(476,520)
Options outstanding, ending (in shares)	4,457,996	3,781,051
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding, beginning weighted-average exercise price (in dollars per share)	$ 29.36
Grants, weighted average exercise price (in dollars per share)	58.97
Forfeitures and Expirations, weighted average exercise price (in dollars per share)	45.76
Exercises, weighted average exercise price (in dollars per share)	27.37
Options outstanding, ending weighted-average exercise price (in dollars per share)	$ 37.41	$ 29.36
Options, outstanding, weighted average remaining contractual term	7 years 2 months 15 days
Options, outstanding intrinsic value	$ 143
Options, exercisable (in shares)	2,372,046
Options, exercisable, weighted average exercise price (in dollars per share)	$ 25.90
Options, exercisable, weighted average remaining contractual term (years)	5 years 11 months 19 days
Options, exercisable, Intrinsic Value	$ 103.4
Options, vested and expected to vest, Outstanding (in shares)	2,056,814
Options, vested and expected to vest, weighted average exercise price (in dollars per share)	$ 50.44
Options, vested and expected to vest, outstanding, weighted average remaining contractual term (in years)	8 years 7 months 9 days
Options, vested and expected to vest, aggregate intrinsic value	$ 39.2
Total intrinsic value of stock options exercised	$ 17	$ 7	$ 2

Equity-Based Compensation - Res

Equity-Based Compensation - Restricted Stock Units ("RSUs") (Details) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested beginning of period (in shares)	1,179,488
Grants (in shares)	25,493
Vested (in shares)	(1,032,821)
Forfeited (in shares)	(41,091)
Nonvested end of period (in shares)	131,069	1,179,488
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning nonvested, weighted average grant date fair value (in dollars per share)	$ 19.52
Granted, weighted average grant date fair value (in dollars per share)	58.90	$ 39.82	$ 36.24
Vested, weighted average grant date fair value (in dollars per share)	17.77
Forfeited, weighted average grant date fair value (in dollars per share	23
Ending nonvested, weighted average grant date fair value (in dollars per share)	$ 40.11	$ 19.52
Vested in period, fair value (less than)	$ 18	$ 1	$ 1

Equity-Based Compensation - Per

Equity-Based Compensation - Performance Share Units ("PSUs") (Details) - Performance Share Units (PSUs) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested beginning of period (in shares)	363,947
Grants (in shares)	254,451
Attainment adjustment (in shares)	361,880
Vested (in shares)	(530,569)
Forfeited (in shares)	(30,736)
Nonvested end of period (in shares)	418,973	363,947
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning nonvested, weighted average grant date fair value (in dollars per share)	$ 38.92
Granted, weighted average grant date fair value (in dollars per share)	59	$ 39.91	$ 37.83
Attainment adjustment (in USD per share)	24.40
Vested, weighted average grant date fair value (in dollars per share)	37.84
Forfeited, weighted average grant date fair value (in dollars per share	47.28
Ending nonvested, weighted average grant date fair value (in dollars per share)	$ 50.75	$ 38.92
Vested in period, fair value (less than)	$ 20	$ 9	$ 0
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential vesting percentage range of shares	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential vesting percentage range of shares	200.00%

Equity-Based Compensation - P84

Equity-Based Compensation - Performance Share Awards ("PSAs") (Details) - Performance Share Awards (PSAs) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested beginning of period (in shares)	246,012
Grants (in shares)	2,714
Vested (in shares)	(121,266)
Forfeited (in shares)	(4,993)
Nonvested end of period (in shares)	122,467	246,012
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning nonvested, weighted average grant date fair value (in dollars per share)	$ 38.96
Granted, weighted average grant date fair value (in dollars per share)	0	$ 40.06	$ 37.79
Vested, weighted average grant date fair value (in dollars per share)	37.79
Forfeited, weighted average grant date fair value (in dollars per share	39.79
Ending nonvested, weighted average grant date fair value (in dollars per share)	$ 40.08	$ 38.96
Vested in period, fair value (less than)	$ 5	$ 0	$ 0
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential vesting percentage range of shares	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential vesting percentage range of shares	200.00%

Equity-Based Compensation - R85

Equity-Based Compensation - Restricted Stock ("RSAs") (Details) - Restricted Stock Awards (RSAs) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested beginning of period (in shares)	26,052
Grants (in shares)	0			3,798,508
Vested (in shares)	(25,398)
Forfeited (in shares)	(654)
Nonvested end of period (in shares)	0	26,052
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning nonvested, weighted average grant date fair value (in dollars per share)	$ 17
Granted, weighted average grant date fair value (in dollars per share)	0
Vested, weighted average grant date fair value (in dollars per share)	17
Forfeited, weighted average grant date fair value (in dollars per share	17
Ending nonvested, weighted average grant date fair value (in dollars per share)	$ 0	$ 17
Vested in period, fair value (less than)	$ 1	$ 1	$ 3
Class B Common Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options nonvested number of shares (in shares)	3,798,508

Equity-Based Compensation - Equ

Equity-Based Compensation - Equity Awards Granted by Seller of CDW UK (Details) $ / shares in Units, $ in Millions	Aug. 01, 2015USD ($)$ / sharesshares
CDW UK
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 35.93
Awards granted at acquisition date, exercise rice (In dollars per share) | $ / shares	$ 0.01
CDW UK
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued during acquisition | shares	1,634,809
Options issued by one of the sellers to certain coworkers over shares of the seller's common stock received as part of consideration from acquisition | shares	608,706
Fair value of options issued by one of the sellers to certain coworkers over shares of the seller's common stock received as part of consideration from acquisition | $	$ 22

Earnings Per Share (Details)

Earnings Per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Basic weighted-average shares outstanding (in shares)	155.4	163.6	170.3
Effect of diluted securities (in shares)	2.8	2.4	1.5
Diluted weighted-average shares outstanding (in shares)	158.2	166	171.8
Antidilutive securities excluded from computation of earnings per share (less than) (in shares)	1	1	1

Coworker Retirement and Other88

Coworker Retirement and Other Compensation Benefits - Profit Sharing and 401(K) Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Defined contribution plan expense	$ 20	$ 23	$ 20

Coworker Retirement and Other89

Coworker Retirement and Other Compensation Benefits - Coworker Stock Purchase Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Coworker Retirement and Other Compensation Benefits [Line Items]
Equity-based compensation expense	$ 43,700,000	$ 39,200,000	$ 31,200,000
Coworker Stock Purchase Plan
Coworker Retirement and Other Compensation Benefits [Line Items]
Employee stock purchase plan discount to market price (as percent)	5.00%
Equity-based compensation expense	$ 0

Coworker Retirement and Other90

Coworker Retirement and Other Compensation Benefits - Restricted Debt Unit Plan (Details) - USD ($) $ in Millions	Sep. 15, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangements [Abstract]
RDU Plan, compensation expense		$ 2	$ 2	$ 5
RDU Plan, obligation payment	$ 31

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Nov. 30, 2015	Aug. 18, 2015	May 22, 2015	Dec. 31, 2015	Aug. 01, 2015
Related Party Transaction [Line Items]
Shares sold by certain selling stockholders (in shares)	9.2	12.9	11.5
Repurchases of common stock (in shares)	1	2.3	2
Share repurchase transaction (in dollars per share)			$ 36.60
Over-Allotment Option
Related Party Transaction [Line Items]
Shares sold by certain selling stockholders (in shares)	1.2	1.7	1.5
CDW UK
Related Party Transaction [Line Items]
Non-controlling interest held					35.00%
Percent of outstanding common stock purchased					65.00%
Net sales from related parties				$ 10

Segment Information - Narrative

Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2017employeesegment
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 - Segment R

Segment Information - Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Income (loss) from operations	221.6	243.7	231.1	169.8	197.2	237.5	223.5	161	866.1	819.2	742
Depreciation and amortization expense									(260.9)	(254.5)	(227.4)
Corporate
Segment Reporting Information [Line Items]
Net sales	1,641.4	1,598.5	1,630.7	1,476.3	1,517.7	1,466.4	1,490.8	1,414.9
Small Business
Segment Reporting Information [Line Items]
Net sales	314.8	311.5	321.5	298.7	291.8	282.5	288.4	277.4
Other
Segment Reporting Information [Line Items]
Net sales	$ 428.3	$ 391	$ 368.1	$ 373.2	$ 350.5	$ 318.7	$ 338.4	$ 355
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net sales									6,347	5,889.8	5,878.7
Income (loss) from operations									487	453.6	432.5
Depreciation and amortization expense									(83.1)	(82.9)	(82.6)
Operating Segments | Small Business
Segment Reporting Information [Line Items]
Net sales									1,246.5	1,140.1	1,089.6
Income (loss) from operations									74.4	68.9	68.3
Depreciation and amortization expense									(20.7)	(20.6)	(20.6)
Operating Segments | Public
Segment Reporting Information [Line Items]
Net sales									6,037.5	5,589.4	5,183.6
Income (loss) from operations									374	368	328.6
Depreciation and amortization expense									(44.8)	(44.7)	(44.7)
Operating Segments | Other
Segment Reporting Information [Line Items]
Net sales									1,560.5	1,362.6	836.8
Income (loss) from operations									57.9	43.6	27.1
Depreciation and amortization expense									(30.9)	(32.1)	(16.2)
Headquarters
Segment Reporting Information [Line Items]
Net sales									0	0	0
Income (loss) from operations									(127.2)	(114.9)	(114.5)
Depreciation and amortization expense									$ (81.4)	$ (74.2)	$ (63.3)

Segment Information - Segment94

Segment Information - Segment Reporting, by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Sales from External Customer [Line Items]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Percentage of Total Net Sales									100.00%	100.00%	100.00%
Total Hardware
Net Sales from External Customer [Line Items]
Net sales									$ 11,941.9	$ 10,987.6	$ 10,289.4
Percentage of Total Net Sales									78.70%	78.60%	79.10%
Notebooks/Mobile Devices
Net Sales from External Customer [Line Items]
Net sales									$ 3,490.9	$ 2,921.6	$ 2,537.3
Percentage of Total Net Sales									23.10%	20.90%	19.50%
Netcomm Products
Net Sales from External Customer [Line Items]
Net sales									$ 2,042.9	$ 1,958.2	$ 1,915
Percentage of Total Net Sales									13.40%	14.00%	14.70%
Desktops
Net Sales from External Customer [Line Items]
Net sales									$ 1,159.4	$ 1,050	$ 965.6
Percentage of Total Net Sales									7.60%	7.50%	7.40%
Video
Net Sales from External Customer [Line Items]
Net sales									$ 1,076.9	$ 962.1	$ 853.8
Percentage of Total Net Sales									7.10%	6.90%	6.60%
Enterprise and Data Storage (Including Drives)
Net Sales from External Customer [Line Items]
Net sales									$ 1,071.5	$ 1,053.1	$ 1,067.2
Percentage of Total Net Sales									7.10%	7.50%	8.20%
Other Hardware
Net Sales from External Customer [Line Items]
Net sales									$ 3,100.3	$ 3,042.6	$ 2,950.5
Percentage of Total Net Sales									20.40%	21.80%	22.70%
Software
Net Sales from External Customer [Line Items]
Net sales									$ 2,540.1	$ 2,389.3	$ 2,152.3
Percentage of Total Net Sales									16.70%	17.10%	16.60%
Services
Net Sales from External Customer [Line Items]
Net sales									$ 611.3	$ 575.1	$ 467.7
Percentage of Total Net Sales									4.00%	4.10%	3.60%
Other
Net Sales from External Customer [Line Items]
Net sales									$ 98.2	$ 29.9	$ 79.3
Percentage of Total Net Sales									0.60%	0.20%	0.70%

Supplemental Guarantor Inform95

Supplemental Guarantor Information - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 144.2	$ 263.7	$ 37.6	$ 344.5
Accounts receivable, net	2,320.5	2,168.6
Merchandise inventory	449.5	452
Miscellaneous receivables	336.5	234.9
Prepaid expenses and other	127.4	118.9
Total current assets	3,378.1	3,238.1
Property and equipment, net	161.1	163.7
Goodwill	2,479.6	2,455	2,500.4	2,217.6
Other intangible assets, net	897	1,055.6
Other assets	40.8	36
Investment in and advances to subsidiaries	0	0
Total Assets	6,956.6	6,948.4
Current liabilities:
Accounts payable-trade	1,317.7	1,072.9
Accounts payable-inventory financing	498	580.4
Current maturities of long-term debt	25.5	18.5
Deferred revenue	194	172.6
Accrued expenses	479.4	436.3
Total current liabilities	2,514.6	2,280.7
Long-term liabilities:
Debt	3,210	3,215.9
Deferred income taxes	196.3	369.2
Other liabilities	52.8	37.1
Total long-term liabilities	3,459.1	3,622.2
Total stockholders’ equity	982.9	1,045.5	1,095.9	936.5
Total Liabilities and Stockholders’ Equity	6,956.6	6,948.4
Reportable Legal Entities | Parent Guarantor
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Merchandise inventory	0	0
Miscellaneous receivables	0	0
Prepaid expenses and other	0	0
Total current assets	0	0
Property and equipment, net	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other assets	1.7	3.2
Investment in and advances to subsidiaries	981.2	1,042.3
Total Assets	982.9	1,045.5
Current liabilities:
Accounts payable-trade	0	0
Accounts payable-inventory financing	0	0
Current maturities of long-term debt	0	0
Deferred revenue	0	0
Accrued expenses	0	0
Total current liabilities	0	0
Long-term liabilities:
Debt	0	0
Deferred income taxes	0	0
Other liabilities	0	0
Total long-term liabilities	0	0
Total stockholders’ equity	982.9	1,045.5
Total Liabilities and Stockholders’ Equity	982.9	1,045.5
Reportable Legal Entities | Subsidiary Issuer
Current assets:
Cash and cash equivalents	113.7	222.7	45.1	346.4
Accounts receivable, net	0	0
Merchandise inventory	0	0
Miscellaneous receivables	103.9	92.6
Prepaid expenses and other	18	14.3
Total current assets	235.6	329.6
Property and equipment, net	95	105.6
Goodwill	751.8	751.8
Other intangible assets, net	280.1	291.5
Other assets	30.7	19.4
Investment in and advances to subsidiaries	3,063.5	3,026.5
Total Assets	4,456.7	4,524.4
Current liabilities:
Accounts payable-trade	42.5	25.9
Accounts payable-inventory financing	1	1.2
Current maturities of long-term debt	14.9	14.9
Deferred revenue	0	0
Accrued expenses	173.3	173.9
Total current liabilities	231.7	215.9
Long-term liabilities:
Debt	3,134.2	3,136.3
Deferred income taxes	66.5	99.1
Other liabilities	43.1	30.8
Total long-term liabilities	3,243.8	3,266.2
Total stockholders’ equity	981.2	1,042.3
Total Liabilities and Stockholders’ Equity	4,456.7	4,524.4
Reportable Legal Entities | Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	0	3.1	0	0
Accounts receivable, net	2,007.7	1,904.9
Merchandise inventory	375.7	390.6
Miscellaneous receivables	205	130.1
Prepaid expenses and other	61.4	69
Total current assets	2,649.8	2,497.7
Property and equipment, net	43.5	49.3
Goodwill	1,439	1,439
Other intangible assets, net	424.5	565.1
Other assets	217.3	248.2
Investment in and advances to subsidiaries	0	0
Total Assets	4,774.1	4,799.3
Current liabilities:
Accounts payable-trade	1,112.1	895.3
Accounts payable-inventory financing	480.9	559.5
Current maturities of long-term debt	3.8	3.6
Deferred revenue	104.5	100.8
Accrued expenses	222.3	214.8
Total current liabilities	1,923.6	1,774
Long-term liabilities:
Debt	8.3	12.1
Deferred income taxes	100.1	205.4
Other liabilities	4.6	3.6
Total long-term liabilities	113	221.1
Total stockholders’ equity	2,737.5	2,804.2
Total Liabilities and Stockholders’ Equity	4,774.1	4,799.3
Reportable Legal Entities | Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	32.4	37.9	31.9	24.6
Accounts receivable, net	312.8	263.7
Merchandise inventory	73.8	61.4
Miscellaneous receivables	27.6	12.2
Prepaid expenses and other	48	35.6
Total current assets	494.6	410.8
Property and equipment, net	22.6	8.8
Goodwill	288.8	264.2
Other intangible assets, net	192.4	199
Other assets	2.6	1.5
Investment in and advances to subsidiaries	0	0
Total Assets	1,001	884.3
Current liabilities:
Accounts payable-trade	165	151.7
Accounts payable-inventory financing	16.1	19.7
Current maturities of long-term debt	6.8	0
Deferred revenue	89.5	71.8
Accrued expenses	83.8	47.7
Total current liabilities	361.2	290.9
Long-term liabilities:
Debt	67.5	67.5
Deferred income taxes	31.4	67.9
Other liabilities	214.9	235.7
Total long-term liabilities	313.8	371.1
Total stockholders’ equity	326	222.3
Total Liabilities and Stockholders’ Equity	1,001	884.3
Reportable Legal Entities | Co-Issuer
Current assets:
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Merchandise inventory	0	0
Miscellaneous receivables	0	0
Prepaid expenses and other	0	0
Total current assets	0	0
Property and equipment, net	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other assets	0	0
Investment in and advances to subsidiaries	0	0
Total Assets	0	0
Current liabilities:
Accounts payable-trade	0	0
Accounts payable-inventory financing	0	0
Current maturities of long-term debt	0	0
Deferred revenue	0	0
Accrued expenses	0	0
Total current liabilities	0	0
Long-term liabilities:
Debt	0	0
Deferred income taxes	0	0
Other liabilities	0	0
Total long-term liabilities	0	0
Total stockholders’ equity	0	0
Total Liabilities and Stockholders’ Equity	0	0
Consolidating Adjustments
Current assets:
Cash and cash equivalents	(1.9)	0	$ (39.4)	$ (26.5)
Accounts receivable, net	0	0
Merchandise inventory	0	0
Miscellaneous receivables	0	0
Prepaid expenses and other	0	0
Total current assets	(1.9)	0
Property and equipment, net	0	0
Goodwill	0	0
Other intangible assets, net	0	0
Other assets	(211.5)	(236.3)
Investment in and advances to subsidiaries	(4,044.7)	(4,068.8)
Total Assets	(4,258.1)	(4,305.1)
Current liabilities:
Accounts payable-trade	(1.9)	0
Accounts payable-inventory financing	0	0
Current maturities of long-term debt	0	0
Deferred revenue	0	0
Accrued expenses	0	(0.1)
Total current liabilities	(1.9)	(0.1)
Long-term liabilities:
Debt	0	0
Deferred income taxes	(1.7)	(3.2)
Other liabilities	(209.8)	(233)
Total long-term liabilities	(211.5)	(236.2)
Total stockholders’ equity	(4,044.7)	(4,068.8)
Total Liabilities and Stockholders’ Equity	$ (4,258.1)	$ (4,305.1)

Supplemental Guarantor Inform96

Supplemental Guarantor Information - Consolidating Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Guarantor Information [Line Items]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Cost of sales									12,741.6	11,654.7	10,872.9
Gross profit	614.4	642	641.1	552.6	577.9	614.3	610.5	524.5	2,449.9	2,327.2	2,115.8
Selling and administrative expenses									1,410.1	1,345.1	1,226
Advertising expense									173.7	162.9	147.8
Income from operations	221.6	243.7	231.1	169.8	197.2	237.5	223.5	161	866.1	819.2	742
Interest (expense) income, net									(150.5)	(146.5)	(159.5)
Net loss on extinguishments of long-term debt									(57.4)	(2.1)	(24.3)
Management fee											0
Gain on remeasurement of equity investment									0	0	98.1
Other income (expense), net									2.1	1.8	(9.3)
Income before income taxes									660.3	672.4	647
Income tax expense									(137.3)	(248)	(243.9)
Income (loss) before equity in earnings of subsidiaries									523	424.4	403.1
Equity in earnings of subsidiaries									0	0	0
Net income	$ 195.2	$ 129.2	$ 141	$ 57.6	$ 103.2	$ 125.9	$ 117.5	$ 77.8	523	424.4	403.1
Reportable Legal Entities | Parent Guarantor
Supplemental Guarantor Information [Line Items]
Net sales									0	0	0
Cost of sales									0	0	0
Gross profit									0	0	0
Selling and administrative expenses									0	0	0
Advertising expense									0	0	0
Income from operations									0	0	0
Interest (expense) income, net									0	0	0
Net loss on extinguishments of long-term debt									0	0	0
Management fee											0
Gain on remeasurement of equity investment											0
Other income (expense), net									0	0	0
Income before income taxes									0	0	0
Income tax expense									(0.9)	0	0
Income (loss) before equity in earnings of subsidiaries									(0.9)	0	0
Equity in earnings of subsidiaries									523.9	424.4	403.1
Net income									523	424.4	403.1
Reportable Legal Entities | Subsidiary Issuer
Supplemental Guarantor Information [Line Items]
Net sales									0	0	0
Cost of sales									0	0	0
Gross profit									0	0	0
Selling and administrative expenses									127.2	114.8	114.5
Advertising expense									0	0	0
Income from operations									(127.2)	(114.8)	(114.5)
Interest (expense) income, net									(148.3)	(145.8)	(158.3)
Net loss on extinguishments of long-term debt									(57.4)	(2.1)	(24.3)
Management fee											4.2
Gain on remeasurement of equity investment											0
Other income (expense), net									(0.1)	0.2	(11.1)
Income before income taxes									(333)	(262.5)	(304)
Income tax expense									149.9	79.9	103.3
Income (loss) before equity in earnings of subsidiaries									(183.1)	(182.6)	(200.7)
Equity in earnings of subsidiaries									707	607	603.8
Net income									523.9	424.4	403.1
Reportable Legal Entities | Guarantor Subsidiaries
Supplemental Guarantor Information [Line Items]
Net sales									13,631	12,619.3	12,151.2
Cost of sales									11,436.1	10,514.4	10,158.6
Gross profit									2,194.9	2,104.9	1,992.6
Selling and administrative expenses									1,093.1	1,057.4	1,020.9
Advertising expense									166.4	157.2	143.2
Income from operations									935.4	890.3	828.5
Interest (expense) income, net									4.1	6.7	2.3
Net loss on extinguishments of long-term debt									0	0	0
Management fee											0
Gain on remeasurement of equity investment											0
Other income (expense), net									0.7	1	1.6
Income before income taxes									940.2	898	832.4
Income tax expense									(269.7)	(319.9)	(307.2)
Income (loss) before equity in earnings of subsidiaries									670.5	578.1	525.2
Equity in earnings of subsidiaries									0	0	0
Net income									670.5	578.1	525.2
Reportable Legal Entities | Non-Guarantor Subsidiaries
Supplemental Guarantor Information [Line Items]
Net sales									1,560.5	1,362.6	837.5
Cost of sales									1,305.5	1,140.3	714.3
Gross profit									255	222.3	123.2
Selling and administrative expenses									189.8	172.9	90.6
Advertising expense									7.3	5.7	4.6
Income from operations									57.9	43.7	28
Interest (expense) income, net									(6.3)	(7.4)	(3.5)
Net loss on extinguishments of long-term debt									0	0	0
Management fee											(4.2)
Gain on remeasurement of equity investment											98.1
Other income (expense), net									1.5	0.6	0.2
Income before income taxes									53.1	36.9	118.6
Income tax expense									(16.6)	(8)	(40)
Income (loss) before equity in earnings of subsidiaries									36.5	28.9	78.6
Equity in earnings of subsidiaries									0	0	0
Net income									36.5	28.9	78.6
Reportable Legal Entities | Co-Issuer
Supplemental Guarantor Information [Line Items]
Net sales									0	0	0
Cost of sales									0	0	0
Gross profit									0	0	0
Selling and administrative expenses									0	0	0
Advertising expense									0	0	0
Income from operations									0	0	0
Interest (expense) income, net									0	0	0
Net loss on extinguishments of long-term debt									0	0	0
Management fee											0
Gain on remeasurement of equity investment											0
Other income (expense), net									0	0	0
Income before income taxes									0	0	0
Income tax expense									0	0	0
Income (loss) before equity in earnings of subsidiaries									0	0	0
Equity in earnings of subsidiaries									0	0	0
Net income									0	0	0
Consolidating Adjustments
Supplemental Guarantor Information [Line Items]
Net sales									0	0	0
Cost of sales									0	0	0
Gross profit									0	0	0
Selling and administrative expenses									0	0	0
Advertising expense									0	0	0
Income from operations									0	0	0
Interest (expense) income, net									0	0	0
Net loss on extinguishments of long-term debt									0	0	0
Management fee											0
Gain on remeasurement of equity investment											0
Other income (expense), net									0	0	0
Income before income taxes									0	0	0
Income tax expense									0	0	0
Income (loss) before equity in earnings of subsidiaries									0	0	0
Equity in earnings of subsidiaries									(1,230.9)	(1,031.4)	(1,006.9)
Net income									$ (1,230.9)	$ (1,031.4)	$ (1,006.9)

Supplemental Guarantor Inform97

Supplemental Guarantor Information - Condensed Consolidated Statements of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Guarantor Information [Line Items]
Comprehensive income	$ 566.7	$ 345.9	$ 358.6
Reportable Legal Entities | Parent Guarantor
Supplemental Guarantor Information [Line Items]
Comprehensive income	566.7	345.9	358.6
Reportable Legal Entities | Subsidiary Issuer
Supplemental Guarantor Information [Line Items]
Comprehensive income	567.6	345.9	358.6
Reportable Legal Entities | Guarantor Subsidiaries
Supplemental Guarantor Information [Line Items]
Comprehensive income	670.5	578.1	525.2
Reportable Legal Entities | Non-Guarantor Subsidiaries
Supplemental Guarantor Information [Line Items]
Comprehensive income	80	(49.6)	34.1
Reportable Legal Entities | Co-Issuer
Supplemental Guarantor Information [Line Items]
Comprehensive income	0	0	0
Consolidating Adjustments
Supplemental Guarantor Information [Line Items]
Comprehensive income	$ (1,318.1)	$ (874.4)	$ (917.9)

Supplemental Guarantor Inform98

Supplemental Guarantor Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	$ 777.7	$ 604	$ 277.5
Cash flows used in investing activities:
Capital expenditures	(81.1)	(63.5)	(90.1)
Premium payments on interest rate cap agreements	0	(2.4)	(0.5)
Acquisition of business, net of cash acquired	0	0	(263.8)
Net cash used in investing activities	(81.1)	(65.9)	(354.4)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	1,560.7	338.8	314.5
Repayments of borrowings under revolving credit facility	(1,560.7)	(338.8)	(314.5)
Repayments of long-term debt	(14.9)	(20.6)	(32.8)
Proceeds from issuance of long-term debt	2,083	1,483	525
Payments to extinguish long-term debt	(2,121.3)	(1,490.4)	(525.3)
Net change in other long-term obligation	(3.8)	15.7	0
Payment of debt financing costs	(9.6)	(5.9)	(6.8)
Net change in accounts payable-inventory financing	(84)	143.6	95.9
Effective portion of interest rate cap agreements	0.4	0	0
Proceeds from stock option exercises	13	7.4	2.4
Proceeds from Coworker Stock Purchase Plan	10.3	9.3	8.7
Repurchases of common stock	(534)	(367.4)	(241.3)
Payment of incentive compensation plan withholding taxes	(49.6)	0	(0.6)
Dividends	(106.9)	(78.7)	(52.9)
Principal payments under capital lease obligations	(1.3)	(0.6)
Repayment of intercompany loan	0	0
Distributions and advances from (to) affiliates	0	0	0
Net cash (used in) provided by financing activities	(818.7)	(304.6)	(226.5)
Effect of exchange rate changes on cash and cash equivalents	2.6	(7.4)	(3.5)
Net (decrease) increase in cash and cash equivalents	(119.5)	226.1	(306.9)
Cash and cash equivalents – beginning of period	263.7	37.6	344.5
Cash and cash equivalents – end of period	144.2	263.7	37.6
Reportable Legal Entities | Parent Guarantor
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	0.6	0	0.5
Cash flows used in investing activities:
Capital expenditures	0	0	0
Premium payments on interest rate cap agreements		0	0
Acquisition of business, net of cash acquired			0
Net cash used in investing activities	0	0	0
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	0	0	0
Repayments of borrowings under revolving credit facility	0	0	0
Repayments of long-term debt	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Payments to extinguish long-term debt	0	0	0
Net change in other long-term obligation	0	0
Payment of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Effective portion of interest rate cap agreements	0
Proceeds from stock option exercises	0	0	0
Proceeds from Coworker Stock Purchase Plan	0	0	0
Repurchases of common stock	(534)	(367.4)	(241.3)
Payment of incentive compensation plan withholding taxes	(49.6)		0
Dividends	(106.9)	(78.7)	(52.9)
Principal payments under capital lease obligations	0	0
Repayment of intercompany loan	0	0
Distributions and advances from (to) affiliates	689.9	446.1	293.7
Net cash (used in) provided by financing activities	(0.6)	0	(0.5)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net (decrease) increase in cash and cash equivalents	0	0	0
Cash and cash equivalents – beginning of period	0	0	0
Cash and cash equivalents – end of period	0	0	0
Reportable Legal Entities | Subsidiary Issuer
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	(71.1)	(158.5)	(18.1)
Cash flows used in investing activities:
Capital expenditures	(55.2)	(50.9)	(75.4)
Premium payments on interest rate cap agreements		(2.4)	(0.5)
Acquisition of business, net of cash acquired			0
Net cash used in investing activities	(55.2)	(53.3)	(75.9)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	1,501.5	329.6	314.5
Repayments of borrowings under revolving credit facility	(1,501.5)	(329.6)	(314.5)
Repayments of long-term debt	(14.9)	(15.2)	(15.4)
Proceeds from issuance of long-term debt	2,083	1,483	525
Payments to extinguish long-term debt	(2,121.3)	(1,490.4)	(525.3)
Net change in other long-term obligation	0	0
Payment of debt financing costs	(9.6)	(4.5)	(6.8)
Net change in accounts payable-inventory financing	(0.2)	1.5	0
Effective portion of interest rate cap agreements	0.4
Proceeds from stock option exercises	13	7.4	2.4
Proceeds from Coworker Stock Purchase Plan	10.3	9.3	8.7
Repurchases of common stock	0	0	0
Payment of incentive compensation plan withholding taxes	0		(0.6)
Dividends	0	0	0
Principal payments under capital lease obligations	0	0
Repayment of intercompany loan	0	0
Distributions and advances from (to) affiliates	56.6	398.3	(196.5)
Net cash (used in) provided by financing activities	17.3	389.4	(207.3)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net (decrease) increase in cash and cash equivalents	(109)	177.6	(301.3)
Cash and cash equivalents – beginning of period	222.7	45.1	346.4
Cash and cash equivalents – end of period	113.7	222.7	45.1
Reportable Legal Entities | Guarantor Subsidiaries
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	788.5	695.5	350
Cash flows used in investing activities:
Capital expenditures	(6.3)	(7.6)	(11.6)
Premium payments on interest rate cap agreements		0	0
Acquisition of business, net of cash acquired			0
Net cash used in investing activities	(6.3)	(7.6)	(11.6)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	0	0	0
Repayments of borrowings under revolving credit facility	0	0	0
Repayments of long-term debt	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Payments to extinguish long-term debt	0	0	0
Net change in other long-term obligation	(3.8)	15.7
Payment of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	(78.4)	131	96.1
Effective portion of interest rate cap agreements	0
Proceeds from stock option exercises	0	0	0
Proceeds from Coworker Stock Purchase Plan	0	0	0
Repurchases of common stock	0	0	0
Payment of incentive compensation plan withholding taxes	0		0
Dividends	0	0	0
Principal payments under capital lease obligations	(0.2)	1
Repayment of intercompany loan	34.3	40.4
Distributions and advances from (to) affiliates	(737.2)	(872.9)	(434.5)
Net cash (used in) provided by financing activities	(785.3)	(684.8)	(338.4)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net (decrease) increase in cash and cash equivalents	(3.1)	3.1	0
Cash and cash equivalents – beginning of period	3.1	0	0
Cash and cash equivalents – end of period	0	3.1	0
Reportable Legal Entities | Non-Guarantor Subsidiaries
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	52.3	56.1	27.9
Cash flows used in investing activities:
Capital expenditures	(19.6)	(5)	(3.1)
Premium payments on interest rate cap agreements		0	0
Acquisition of business, net of cash acquired			(263.8)
Net cash used in investing activities	(19.6)	(5)	(266.9)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	59.2	9.2	0
Repayments of borrowings under revolving credit facility	(59.2)	(9.2)	0
Repayments of long-term debt	0	(5.4)	(17.4)
Proceeds from issuance of long-term debt	0	0	0
Payments to extinguish long-term debt	0	0	0
Net change in other long-term obligation	0	0
Payment of debt financing costs	0	(1.4)	0
Net change in accounts payable-inventory financing	(5.4)	11.1	(0.2)
Effective portion of interest rate cap agreements	0
Proceeds from stock option exercises	0	0	0
Proceeds from Coworker Stock Purchase Plan	0	0	0
Repurchases of common stock	0	0	0
Payment of incentive compensation plan withholding taxes	0		0
Dividends	0	0	0
Principal payments under capital lease obligations	(1.1)	(1.6)
Repayment of intercompany loan	(34.3)	(40.4)
Distributions and advances from (to) affiliates	0	0	267.4
Net cash (used in) provided by financing activities	(40.8)	(37.7)	249.8
Effect of exchange rate changes on cash and cash equivalents	2.6	(7.4)	(3.5)
Net (decrease) increase in cash and cash equivalents	(5.5)	6	7.3
Cash and cash equivalents – beginning of period	37.9	31.9	24.6
Cash and cash equivalents – end of period	32.4	37.9	31.9
Reportable Legal Entities | Co-Issuer
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	0	0	0
Cash flows used in investing activities:
Capital expenditures	0	0	0
Premium payments on interest rate cap agreements		0	0
Acquisition of business, net of cash acquired			0
Net cash used in investing activities	0	0	0
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	0	0	0
Repayments of borrowings under revolving credit facility	0	0	0
Repayments of long-term debt	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Payments to extinguish long-term debt	0	0	0
Net change in other long-term obligation	0	0
Payment of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Effective portion of interest rate cap agreements	0
Proceeds from stock option exercises	0	0	0
Proceeds from Coworker Stock Purchase Plan	0	0	0
Repurchases of common stock	0	0	0
Payment of incentive compensation plan withholding taxes	0		0
Dividends	0	0	0
Principal payments under capital lease obligations	0	0
Repayment of intercompany loan	0	0
Distributions and advances from (to) affiliates	0	0	0
Net cash (used in) provided by financing activities	0	0	0
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net (decrease) increase in cash and cash equivalents	0	0	0
Cash and cash equivalents – beginning of period	0	0	0
Cash and cash equivalents – end of period	0	0	0
Consolidating Adjustments
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	7.4	10.9	(82.8)
Cash flows used in investing activities:
Capital expenditures	0	0	0
Premium payments on interest rate cap agreements		0	0
Acquisition of business, net of cash acquired			0
Net cash used in investing activities	0	0	0
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facility	0	0	0
Repayments of borrowings under revolving credit facility	0	0	0
Repayments of long-term debt	0	0	0
Proceeds from issuance of long-term debt	0	0	0
Payments to extinguish long-term debt	0	0	0
Net change in other long-term obligation	0	0
Payment of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Effective portion of interest rate cap agreements	0
Proceeds from stock option exercises	0	0	0
Proceeds from Coworker Stock Purchase Plan	0	0	0
Repurchases of common stock	0	0	0
Payment of incentive compensation plan withholding taxes	0		0
Dividends	0	0	0
Principal payments under capital lease obligations	0	0
Repayment of intercompany loan	0	0
Distributions and advances from (to) affiliates	(9.3)	28.5	69.9
Net cash (used in) provided by financing activities	(9.3)	28.5	69.9
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net (decrease) increase in cash and cash equivalents	(1.9)	39.4	(12.9)
Cash and cash equivalents – beginning of period	0	(39.4)	(26.5)
Cash and cash equivalents – end of period	$ (1.9)	$ 0	$ (39.4)

Selected Quarterly Financial 99

Selected Quarterly Financial Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Gross profit	614.4	642	641.1	552.6	577.9	614.3	610.5	524.5	2,449.9	2,327.2	2,115.8
Income (loss) from operations	221.6	243.7	231.1	169.8	197.2	237.5	223.5	161	866.1	819.2	742
Net income	$ 195.2	$ 129.2	$ 141	$ 57.6	$ 103.2	$ 125.9	$ 117.5	$ 77.8	$ 523	$ 424.4	$ 403.1
Earnings per share, basic (in dollars per share)	$ 1.28	$ 0.84	$ 0.90	$ 0.36	$ 0.64	$ 0.78	$ 0.71	$ 0.47	$ 3.37	$ 2.59	$ 2.37
Earnings per share, diluted (in dollars per share)	1.26	0.83	0.89	0.35	0.63	0.76	0.70	0.46	3.31	2.56	2.35
Cash dividends declared per common share (in dollars per share)	$ 0.2100	$ 0.1600	$ 0.1600	$ 0.1600	$ 0.1600	$ 0.1075	$ 0.1075	$ 0.1075	$ 0.6900	$ 0.4825	$ 0.3100
Corporate
Segment Reporting Information [Line Items]
Net sales	$ 1,641.4	$ 1,598.5	$ 1,630.7	$ 1,476.3	$ 1,517.7	$ 1,466.4	$ 1,490.8	$ 1,414.9
Small Business
Segment Reporting Information [Line Items]
Net sales	314.8	311.5	321.5	298.7	291.8	282.5	288.4	277.4
Public
Segment Reporting Information [Line Items]
Net sales	1,454.1	1,732.9	1,674.1	1,176.5	1,332.3	1,640.6	1,547	1,069.4
Public | Government
Segment Reporting Information [Line Items]
Net sales	630	606.7	543.9	386.9	529.6	537.5	456.6	339.9
Public | Education
Segment Reporting Information [Line Items]
Net sales	400.8	700.7	712.9	397.1	365.9	671.4	640	341
Public | Healthcare
Segment Reporting Information [Line Items]
Net sales	423.3	425.5	417.3	392.5	436.8	431.7	450.4	388.5
Other
Segment Reporting Information [Line Items]
Net sales	$ 428.3	$ 391	$ 368.1	$ 373.2	$ 350.5	$ 318.7	$ 338.4	$ 355

Subsequent Events (Details)

Subsequent Events (Details)	Feb. 07, 2018$ / shares
Subsequent Event
Subsequent Event [Line Items]
Quarterly cash dividend, declared (in dollars per share)	$ 0.21

Schedule II - Valuation And 101

Schedule II - Valuation And Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts:
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 5.9	$ 6	$ 5.7
Charged to Costs and Expenses	2.1	2	4.2
Deductions	(1.8)	(2.1)	(3.9)
Balance at End of Period	6.2	5.9	6
Reserve for sales returns:
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	6.8	4.9	5.1
Charged to Costs and Expenses	40.6	38.1	34.4
Deductions	(41)	(36.2)	(34.6)
Balance at End of Period	$ 6.4	$ 6.8	$ 4.9