CDW (CDW) 10-K 26 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 20, 2015	Jun. 30, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	CDW Corp
Entity Central Index Key	1402057
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
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			$2,762,305,595
Entity Common Stock, Shares Outstanding		172,275,656

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets:
Cash and cash equivalents	$344.50	$188.10
Accounts receivable, net of allowance for doubtful accounts	1,561.10	1,451
Merchandise inventory	337.5	382
Miscellaneous receivables	155.6	146.3
Prepaid expenses and other	54.7	46.1
Total current assets	2,453.40	2,213.50
Property and equipment, net	137.2	131.1
Equity Method Investments	86.7	0
Goodwill	2,217.60	2,220.30
Other intangible assets, net	1,168.80	1,328
Deferred financing costs, net	33	30.1
Other assets	3.2	1.6
Total assets	6,099.90	5,924.60
Current Liabilities:
Accounts payable-trade	704	662.8
Accounts payable-inventory financing	332.1	256.6
Current maturities of long-term debt	15.4	45.4
Deferred revenue	81.3	94.8
Accrued expenses:
Compensation	130.1	112.2
Interest	28.1	31.8
Sales taxes	29.1	29.2
Advertising	34	33.2
Income taxes	0.2	6.3
Other	113.7	130.3
Total current liabilities	1,468	1,402.60
Long-term liabilities:
Debt	3,174.60	3,205.80
Deferred income taxes	475	563.5
Other liabilities	45.8	41
Total long-term liabilities	3,695.40	3,810.30
Commitments and contingencies
Shareholders' deficit:
Preferred Stock, Value, Issued	0	0
Common shares	1.7	1.7
Paid-in capital	2,711.90	2,688.10
Accumulated deficit	-1,760.50	-1,971.80
Accumulated other comprehensive loss	-16.6	-6.3
Total shareholders' deficit	936.5	711.7
Total liabilities and shareholders' deficit	$6,099.90	$5,924.60

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets Parenthetical (Parentheticals) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, except Per Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Allowance for Doubtful Accounts Receivable, Current	$5.70	$5.40
Preferred Stock, Par or Stated Value Per Share	$0.01	$0.01
Preferred Stock, Shares Authorized	100	100
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share	$0.01	$0.01
Common Stock, Shares Authorized	1,000	1,000
Common Stock, Shares, Issued	172.2	172
Common Stock, Shares, Outstanding	172.2	172

Consolidated_Statements_Of_Ope

Consolidated Statements Of Operations (USD $)	3 Months Ended																12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Net Sales	$3,050.10		$3,266.10		$3,106		$2,652.30		$2,713.30		$2,864.30		$2,779.30		$2,411.70		$12,074.50	$10,768.60		$10,128.20
Cost of sales																	10,153.20	9,008.30		8,458.60
Gross profit	491.9		507.3		496.9		425.2		448.3		458.4		451.6		402		1,921.30	1,760.30		1,669.60
Selling and administrative expenses																	1,110.30	1,120.90		1,029.50
Advertising expense																	138	130.8		129.5
Income (loss) from operations	164.3		184.7		188.2		135.8		142	[1]	92.9	[1]	153.6	[1]	120.1	[1]	673	508.6	[2]	510.6
Interest expense, net																	-197.3	-250.1		-307.4
Net (loss) gain on extinguishments of long-term debt																	-90.7	-64		-17.2
Other income, net																	2.7	1		0.1
Income (loss) before income taxes																	387.7	195.5		186.1
Income tax (expense) benefit																	-142.8	-62.7		-67.1
Net income (loss)	$51.80		$55.60		$86.60		$50.90		$60	[1]	($2.20)	[1]	$46.70	[1]	$28.30	[1]	$244.90	$132.80		$119
Basic	$0.30	[3]	$0.33	[3]	$0.51	[3]	$0.30	[3]	$0.35	[1],[3]	($0.01)	[1],[3]	$0.32	[1],[3]	$0.19	[1],[3]	$1.44	$0.85		$0.82
Diluted	$0.30	[3]	$0.32	[3]	$0.50	[3]	$0.30	[3]	$0.35	[1],[3]	($0.01)	[1],[3]	$0.32	[1],[3]	$0.19	[1],[3]	$1.42	$0.84		$0.82
Basic																	170.6	156.6		145.1
Diluted																	172.8	158.7		145.8
Common Stock, Dividends, Per Share, Declared																	$0.20	$0.04		$0
[1]	(3)The third quarter of 2013 included pre-tax IPO-related charges of $74.1 million. See Note 9 for additional discussion of the IPO.
[2]	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.
[3]	(1) Basic and diluted net income (loss) 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 (loss) per share.

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Loss) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income (loss)	$244.90	$132.80	$119
Foreign currency translation adjustment	-10.3	-6.7	2.5
Other Comprehensive Income (Loss), Net of Tax	-10.3	-6.7	2.5
Comprehensive income (loss)	$234.60	$126.10	$121.50

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Loss) Parenthetical (Parentheticals) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	$0.50	$0	$0

Consolidated_Statement_Of_Shar

Consolidated Statement Of Shareholders' (Deficit) Equity (USD $)	Total	Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Preferred Stock [Member]	Common Stock [Member]
In Millions, except Share data
Balance at at Dec. 31, 2011	($7.30)	$2,184.70	($2,191.30)	($2.10)	$0	$1.40
Preferred Stock, Shares Issued at Dec. 31, 2011					0
Common Stock, Shares, Issued at Dec. 31, 2011						144,900,000
Equity-based compensation expense	22.1	22.1	0	0	0	0
Investment from CDW Holdings LLC	2.8	2.8	0	0	0	0
Repurchase of Class B Common Shares	-0.7	0	-0.7	0	0	0
Treasury Stock, Shares, Acquired						0
Accrued charitable contribution related to the MPK Coworker Incentive Plan II, net of tax	-1.4	-1.4	0	0	0	0
Stock Issued During Period, Shares, Accrued Charitable Contribution related to the MPK Coworker Incentive Plan II						300,000
MPK Coworker Incentive Plan II units withheld for taxes	-0.5	-0.5	0	0	0	0
Net income (loss)	119	0	119	0	0	0
Foreign currency translation adjustment	2.5	0	0	2.5	0	0
Balance at at Dec. 31, 2012	136.5	2,207.70	-2,073	0.4	0	1.4
Preferred Stock, Shares Issued at Dec. 31, 2012					0
Common Stock, Shares, Issued at Dec. 31, 2012						145,200,000
Equity-based compensation expense		46.6	0	0	0	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Stock Options, Requisite Service Period Recognition	46.6
Stock Issued During Period, Value, New Issues	424.7	424.4	0	0	0	0.3
Stock Issued During Period, Shares, New Issues						26,800,000
Repurchase of Class B Common Shares	-0.2	0	-0.2	0	0	0
Dividends, Common Stock	-7.3	0	-7.3		0	0
Reclassification to goodwill for accrued charitable contributions	9.4	9.4	0	0	0	0
MPK Coworker Incentive Plan II units withheld for taxes	-24.1	0	-24.1	0	0	0
Stock Issued During Period, Shares, Incentive Compensation Plan units withheld for taxes						0
Net income (loss)	132.8	0	132.8	0	0	0
Foreign currency translation adjustment	-6.7	0	0	-6.7	0	0
Balance at at Dec. 31, 2013	711.7	2,688.10	-1,971.80	-6.3	0	1.7
Preferred Stock, Shares Issued at Dec. 31, 2013	0				0
Common Stock, Shares, Issued at Dec. 31, 2013	172,000,000					172,000,000
Equity-based compensation expense	16.4	16.4	0	0	0	0
Stock Issued During Period, Value, Stock Options Exercised	1.3	1.3	0	0	0	0
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	0.3	0.3	0	0	0	0
Stock Issued During Period, Shares, Employee Stock Purchase Plans						200,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	-5.8	-5.8	0	0	0	0
Dividends, Common Stock	-33.6	0	-33.6	0	0	0
Net income (loss)	244.9	0	244.9	0	0	0
Foreign currency translation adjustment	-10.3	0	0	-10.3	0	0
Balance at at Dec. 31, 2014	$936.50	$2,711.90	($1,760.50)	($16.60)	$0	$1.70
Preferred Stock, Shares Issued at Dec. 31, 2014	0				0
Common Stock, Shares, Issued at Dec. 31, 2014	172,200,000					172,200,000

Consolidated_Statements_Of_Cas

Consolidated Statements Of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income (loss)	$244.90	$132.80	$119
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	207.9	208.2	210.2
Equity-based compensation expense	16.4	46.6	22.1
Deferred income taxes	-89.1	-48.7	-56.3
Allowance for doubtful accounts	0.3	0	0
Amortization of deferred financing costs	6.4	8.8	13.6
Net (loss) gain on extinguishments of long-term debt	90.7	64	17.2
Income (Loss) from Equity Method Investments	-1.2	0	0
Other Operating Activities, Cash Flow Statement	0.5	1.7	1
Changes in assets and liabilities:
Accounts receivable	-117.6	-170.8	-10.4
Merchandise inventory	44.2	-67.5	7.1
Other assets	-18.7	-10.1	-3.8
Increase (Decrease) in Accounts Payable, Trade	43.7	146.1	0.8
Other current liabilities	1.7	64.1	-2.1
Long-term liabilities	4.9	-8.9	-1
Net cash provided by operating activities	435	366.3	317.4
Cash flows from investing activities:
Capital expenditures	-55	-47.1	-41.4
Payments to Acquire Equity Method Investments	-86.8	0	0
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	-20.9	0	0
Premium payments on interest rate cap agreements	-2.1	0	-0.3
Net cash used in investing activities	-164.8	-47.1	-41.7
Cash flows from financing activities:
Proceeds from borrowings under revolving credit facility	0	63	289
Repayments of borrowings under revolving credit facility	0	-63	-289
Repayments of long-term debt	-15.4	-51.1	-201
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Payments to extinguish long-term debt	-1,299	-2,047.40	-243.2
Payments of debt financing costs	-21.9	-6.1	-2.1
Investment from CDW Holdings LLC	0	0	2.8
Net change in accounts payable-inventory financing	75.5	7.4	-29.5
Net proceeds from issuance of common shares	0	424.7	0
Proceeds from Stock Options Exercised	1.3	0	0
Proceeds from Coworker Stock Purchase Plan	5.8	0	0
Dividends paid	-33.6	-7.3	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0.3	0.6	0
Payment of incentive compensation plan withholding taxes	0	-24.1	0
Repurchase of common shares	0	-0.2	-0.7
Net cash used in financing activities	-112	-168.3	-338
Effect of exchange rate changes on cash and cash equivalents	-1.8	-0.7	0.3
Net increase (decrease) in cash and cash equivalents	156.4	150.2	-62
Cash and cash equivalents - beginning of period	188.1	37.9	99.9
Cash and cash equivalents - end of period	344.5	188.1	37.9
Supplementary disclosure of cash flow information:
Interest paid, including cash settlements on interest rate swap agreements	-195.8	-267.6	-302.7
Taxes refunded (paid), net	-241.2	-82.5	-123.2
Non-cash investing and financing activities:
Capital expenditures accrued in accounts payable-trade	$0.60	$0.20	$0.50

Description_Of_Business_And_Su

Description Of Business And Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Description of Business and Summary of Significant 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 and a leading provider of integrated information technology (“IT”) solutions to small, medium and large business, government, education and healthcare customers in the U.S. 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. On August 6, 2010, CDW Finance Corporation, a Delaware corporation, was formed for the sole purpose of acting as co-issuer of certain debt obligations as described in Note 18 and does not hold any material assets or engage in any business activities or operations.
	CDW Corporation was previously owned directly by CDW Holdings LLC ("CDW Holdings"), a company controlled by investment funds affiliated with Madison Dearborn Partners, LLC ("Madison Dearborn") and Providence Equity Partners L.L.C. ("Providence Equity," and together with Madison Dearborn, the "Sponsors"), certain other co-investors and certain members of CDW management. On July 2, 2013, Parent completed an initial public offering ("IPO") of its common stock. In connection with the IPO, CDW Holdings distributed all of its shares of Parent's common stock to its members in June 2013 in accordance with the members’ respective membership interests and was subsequently dissolved in August 2013. See Note 9 for additional discussion of the IPO.
	Basis of Presentation
	The accompanying 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 U.S. Securities and Exchange Commission (“SEC”).
	Principles of Consolidation
	The accompanying 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 at 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.
	Cash and Cash Equivalents
	Cash and cash equivalents include all deposits in banks and short-term (original maturities of three months or less), 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.
	Merchandise Inventory
	Inventory is valued at the lower of cost or market 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 estimated market 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 generally consist of amounts due from vendors. The Company receives incentives from vendors related to cooperative advertising allowances, 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 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. Leasehold improvements are amortized over the shorter of their 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 following table shows estimated useful lives of property and equipment:
	Classification	Estimated
		Useful Lives
	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 operating leases to its original condition upon lease termination. The Company’s asset retirement liability was $0.5 million as of December 31, 2014 and 2013.
	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 net income or loss of equity method investees is included in other income, net in the consolidated statements of operations.
	Goodwill and Other Intangible Assets
	The Company is required to perform an evaluation of goodwill on an annual basis 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 used to assess potential goodwill impairment are the same as its operating segments. The Company has the option of performing a qualitative assessment of a reporting unit's fair value from the last quantitative assessment to determine if it is more likely than not that the reporting unit's goodwill is impaired or performing a quantitative assessment by comparing a reporting unit's estimated fair value to its carrying amount. Under the quantitative assessment, testing for impairment of goodwill is a two-step process. The first step compares the fair value of a reporting unit with its carrying amount, including goodwill. If the carrying amount of a reporting unit exceeds its fair value, the second step compares the implied fair value of reporting unit goodwill with the carrying amount of that goodwill to determine the amount of impairment loss. Fair value of a reporting unit is determined by using a weighted combination of an income approach and a market approach, as this combination is considered the most indicative of the Company’s fair value in an orderly transaction between market participants. This assessment uses significant accounting judgments, estimates and assumptions. Any changes in the judgments, estimates or assumptions used could produce significantly different results. During the years ended December 31, 2014, 2013 and 2012, the Company concluded its goodwill was not impaired. See Note 4 for more information on the Company’s evaluations of goodwill for impairment.
	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. These intangible assets are reviewed for impairment when indicators are present using undiscounted cash flows. The Company uses the undiscounted cash flows, excluding interest charges, to assess the recoverability of the carrying value of such assets. To the extent carrying value exceeds the undiscounted cash flows, an impairment loss is recorded based upon the excess of the carrying value over 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. During the years ended December 31, 2014, 2013 and 2012, no impairment existed with respect to the Company’s intangible assets with determinable lives and no significant changes to the remaining useful lives were necessary. The following table shows estimated useful lives of definite-lived intangible assets:
	Classification	Estimated
		Useful Lives
	Customer relationships	11 to 14 years
	Trade name	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 over the estimated life of the related debt instrument using the effective interest method or straight-line method, as applicable.
	Derivatives
	The Company has entered into interest rate cap agreements for the purpose of economically hedging its exposure to fluctuations in interest rates. These derivatives are recorded at fair value in the Company’s consolidated balance sheets.
	The Company’s interest rate cap agreements are not designated as cash flow hedges of interest rate risk. Changes in fair value of the derivatives are recorded directly to interest expense in the Company’s consolidated statements of operations.
	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) Income
	Foreign currency translation adjustments are included in shareholders’ equity under accumulated other comprehensive (loss) income.
	The components of accumulated other comprehensive (loss) income are as follows:
	(in millions)	December 31,
		2014			2013			2012
	Foreign currency translation adjustment	$	(16.6	)	$	(6.3	)	$	0.4
	Accumulated other comprehensive (loss) income	$	(16.6	)	$	(6.3	)	$	0.4
	Revenue Recognition
	The Company is a primary distribution channel for a large group of vendors and suppliers, including original equipment manufacturers (“OEMs”), software publishers and wholesale distributors. 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 products and 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 or recognized using a proportional performance model for services provided at a fixed fee. Revenue from cloud computing solutions including Software as a Service ("SaaS") and Infrastructure as a Service ("IaaS") arrangements, as well as data center services such as managed and remote managed services, server co-location, internet connectivity and data backup and storage, is 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.
From time to time, the Company 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. 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 (1) payments received from customers in advance of providing the product or performing services, and (2) 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 Company’s 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 typically recognized in the period incurred at the applicable interest rate in effect. For increasing-rate debt, the Company determines the periodic interest cost using the effective interest method over the estimated outstanding term of the debt. The difference between interest expense recorded and cash interest paid is reflected as short-term or long-term accrued interest in the Company’s consolidated balance sheets.
Foreign Currency Translation
The Company’s functional currency is the U.S. dollar. The functional currency of the Company’s Canadian subsidiary is the local currency, the Canadian dollar. The functional currency of the Company's equity investment in Kelway TopCo Limited ("Kelway") is the local currency, the British pound sterling.  Assets and liabilities of the Canadian subsidiary and the Company’s share of assets and liabilities in Kelway are translated at the spot rate in effect at the applicable reporting date and the consolidated results of operations of the Canadian subsidiary and the Company’s share of the net income or loss of Kelway 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) income, which is reflected as a separate component of shareholders’ 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.

Recent_Accounting_Pronouncemen

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	Stock Compensation - Performance Share Awards
	In June 2014, the Financial Accounting Standards Board (the "FASB") issued Accounting Standards Update ("ASU") 2014-12, “Compensation - Stock Compensation,” which amended the standard on how to account for share-based payments when the terms of an award provide that a performance target could be achieved after the requisite service period. Under this ASU, a performance target that could be achieved after the requisite service period is required to be treated as a performance condition that affects the vesting of the award and should not be reflected in estimating the fair value of the award at the grant date. This ASU is effective for the first quarter of 2016 with early adoption permitted. The Company already accounts for performance shares utilizing the method outlined by this ASU and is not impacted by the new standard.
	Revenue Recognition
	In May 2014, the FASB issued ASU 2014-09, "Revenue from Contracts with Customers," which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes the most current revenue recognition standard. This ASU is effective for the Company for the first quarter of 2017 and early adoption is not permitted. This ASU allows for either a full retrospective adoption approach or a modified retrospective adoption approach. The Company is currently evaluating the impact that this ASU will have on its consolidated financial position, results of operations and cash flows.

Property_And_Equipment

Property And Equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property And Equipment	Property and Equipment
	Property and equipment consisted of the following:
	(in millions)	December 31,
		2014		2013
	Land	$	27.7	$	27.7
	Machinery and equipment	54.3		53
	Building and leasehold improvements	105.1		104.8
	Computer and data processing equipment	65.6		61.2
	Computer software	10.6		30.9
	Furniture and fixtures	21.7		21.6
	Construction in progress	24.7		10.9
	Property and equipment	309.7		310.1
	Less: accumulated depreciation	172.5		179
	Property and equipment, net	$	137.2	$	131.1
	During 2014, 2013 and 2012, the Company recorded disposals of $32.0 million, $7.9 million and $12.2 million, respectively, to remove assets that were no longer in use from property and equipment. The Company recorded a pre-tax loss of $0.1 million, $0.0 million and $0.1 million in 2014, 2013 and 2012, respectively, for certain disposed assets that were not fully depreciated.
	Depreciation expense for the years ended December 31, 2014, 2013 and 2012 was $25.8 million, $27.2 million and $32.0 million, respectively.

Goodwill_And_Other_Intangible_

Goodwill And Other Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill And Other Intangible Assets	Goodwill and Other Intangible Assets
	As described in Note 1, the Company is required to perform an evaluation of goodwill on an annual basis 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 used to assess potential goodwill impairment are the same as its operating segments. The Company has two reportable segments: Corporate, which is comprised primarily of business customers, and Public, which is comprised of government entities and education and healthcare institutions. The Company also has three other operating segments, CDW Advanced Services, Canada, and Kelway, which do not meet the reportable segment quantitative thresholds and, accordingly, are combined together as “Other” for segment reporting purposes. The Company has the option of performing a qualitative assessment of a reporting unit's fair value from the last quantitative assessment to determine if it is more likely than not that the reporting unit's goodwill is impaired or performing a quantitative assessment by comparing a reporting unit's estimated fair value to its carrying amount. Under the quantitative assessment, testing for impairment of goodwill is a two-step process. The first step compares the fair value of a reporting unit with its carrying amount, including goodwill. If the carrying amount of a reporting unit exceeds its fair value, the second step compares the implied fair value of reporting unit goodwill with the carrying amount of that goodwill to determine the amount of impairment loss. Fair value of a reporting unit is determined by using a weighted combination of an income approach and a market approach, 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 determined 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. Under the market approach, the Company utilized 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 were 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 revenue growth rates, gross margins, operating margins, discount rates and future market conditions, among others.
	December 1, 2014 Evaluation
	The Company performed its annual evaluation of goodwill as of December 1, 2014 by utilizing a quantitative assessment for all reporting units. All reporting units passed the first step of the goodwill evaluation (with the fair value exceeding the carrying value by 169%, 147%, 276% and 78% for the Corporate, Public, Canada and CDW Advanced Services reporting units, respectively) and, accordingly, the Company was not required to perform the second step of the goodwill evaluation.
	To determine the fair value of the reporting units, the Company used a 75%/25% weighting of the income approach and market approach, respectively. Under the income approach, the Company estimated future cash flows of each reporting unit based on internally generated forecasts for the remainder of 2014 and the next six years. The Company used a 3.5% long-term assumed consolidated annual revenue growth rate for periods after the six-year forecast. The estimated future cash flows for the Corporate and Public reporting units were discounted at 9.0%; cash flows for the Canada and CDW Advanced Services reporting units were discounted at 9.3% and 11.5%, respectively, based on the future growth rates assumed in the discounted cash flows. Discount rates utilized during the 2014 goodwill evaluation declined compared to those used in 2013 as a result of the market performance of the Company's common stock and a lower equity risk premium with the exception of CDW Advanced Services. The discount rate for CDW Advanced Services increased to account for additional forecast risk.
	December 1, 2013 Evaluation
	The Company performed its annual evaluation of goodwill as of December 1, 2013 by utilizing a quantitative assessment for all reporting units. All reporting units passed the first step of the goodwill evaluation (with the fair value exceeding the carrying value by 107%, 82%, 167% and 168% for the Corporate, Public, Canada and CDW Advanced Services reporting units, respectively) and, accordingly, the Company was not required to perform the second step of the goodwill evaluation.
	To determine the fair value of the reporting units, the Company used a 75%/25% weighting of the income approach and market approach, respectively. Under the income approach, the Company estimated future cash flows of each reporting unit based on internally generated forecasts for the remainder of 2013 and the next six years. The Company used a 3.5% long-term assumed consolidated annual revenue growth rate for periods after the six-year forecast. The estimated future cash flows for the Corporate and Public reporting units were discounted at 10.0%; cash flows for the Canada and CDW Advanced Services reporting units were discounted at 10.3% and 10.5%, respectively, based on the future growth rates assumed in the discounted cash flows. Discount rates utilized during the 2013 goodwill evaluation declined compared to those used in 2012 as a result of the market performance of the Company's common stock and a lower equity risk premium.
	December 1, 2012 Evaluation
	The Company performed its annual evaluation of goodwill as of December 1, 2012 by utilizing a quantitative assessment for all reporting units. All reporting units passed the first step of the goodwill evaluation (with the fair value exceeding the carrying value by 49%, 44%, 104% and 17% for the Corporate, Public, Canada and CDW Advanced Services reporting units, respectively) and, accordingly, the Company was not required to perform the second step of the goodwill evaluation.
	To determine the fair value of the reporting units, the Company used a 75%/25% weighting of the income approach and market approach, respectively. Under the income approach, the Company estimated future cash flows of each reporting unit based on internally generated forecasts for the remainder of 2012 and the next six years. The Company used a 3.5% long-term assumed consolidated annual revenue growth rate for periods after the six-year forecast. The estimated future cash flows for the Corporate and Public reporting units were discounted at 11.5%; cash flows for the Canada and CDW Advanced Services reporting units were discounted at 11.8% and 12.0%, respectively, based on the future growth rates assumed in the discounted cash flows.
	The following table presents the change in goodwill by segment for the years ended December 31, 2014 and 2013:
	(in millions)	Corporate			Public			Other (1)			Consolidated
	Balances as of December 31, 2012:
	Goodwill	$	2,794.40		$	1,261.40		$	107.3		$	4,163.10
	Accumulated impairment charges	(1,571.4		)	(354.1		)	(28.3		)	(1,953.8		)
		$	1,223.00		$	907.3		$	79		$	2,209.30
	2013 Activity:
	Translation adjustment	$	—		$	—		$	(2.1	)	$	(2.1	)
	Contingent consideration (2)	8.8			4			0.3			13.1
		$	8.8		$	4		$	(1.8	)	$	11
	Balances as of December 31, 2013:
	Goodwill	$	2,803.20		$	1,265.40		$	105.5		$	4,174.10
	Accumulated impairment charges	(1,571.4		)	(354.1		)	(28.3		)	(1,953.8		)
		$	1,231.80		$	911.3		$	77.2		$	2,220.30
	2014 Activity:
	Translation adjustment	$	—		$	—		$	(2.7	)	$	(2.7	)
		$	—		$	—		$	(2.7	)	$	(2.7	)
	Balances as of December 31, 2014:
	Goodwill	$	2,803.20		$	1,265.40		$	102.8		$	4,171.40
	Accumulated impairment charges	(1,571.4		)	(354.1		)	(28.3		)	(1,953.8		)
		$	1,231.80		$	911.3		$	74.5		$	2,217.60
	-1	Other is comprised of CDW Advanced Services, Canada, and Kelway reporting units. There is no goodwill attributable to the Kelway reporting unit.
	-2	During 2013, the Company recorded a $13.1 million net-of-tax addition to goodwill in connection with the settlement of the MPK Coworker Incentive Plan II and related charitable contribution. The charitable contribution was accounted for as additional purchase price (goodwill) in accordance with pre-2009 business combinations accounting guidance. See Note 10 for additional discussion of this transaction.
	The following table presents a summary of intangible assets at December 31, 2014 and 2013:
	(in millions)
	December 31, 2014		Gross			Accumulated			Net Carrying Amount
			Carrying			Amortization
			Amount
	Customer relationships		$	1,859.70		$	1,012.10		$	847.6
	Trade name		421			152			269
	Internally developed software		110.1			58.9			51.2
	Other		3.2			2.2			1
	Total		$	2,394.00		$	1,225.20		$	1,168.80
	December 31, 2013
	Customer relationships		$	1,860.80		$	872.8		$	988
	Trade name		421			130.9			290.1
	Internally developed software		128.5			79.8			48.7
	Other		3.1			1.9			1.2
	Total		$	2,413.40		$	1,085.40		$	1,328.00
	During 2014, the Company recorded disposals of $41.7 million to remove fully amortized internally developed software assets that were no longer in use from intangible assets.
	Amortization expense related to intangible assets for the years ended December 31, 2014, 2013 and 2012 was $182.1 million, $181.0 million and $178.2 million, respectively.
	Estimated future amortization expense related to intangible assets for the next five years is as follows:
	(in millions)
	Years ending December 31,
	2015	$	180.7
	2016	172.8
	2017	167.1
	2018	160.4
	2019	158.9

Inventory_Financing_Agreements

Inventory Financing Agreements	12 Months Ended
	Dec. 31, 2014
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 accompanying consolidated balance sheets. The Company does not incur any interest expense associated with these agreements as balances are paid when they are due.
	The following table presents the amounts included in accounts payable-inventory financing:
	(in millions)	December 31,
		2014		2013
	Revolving Loan inventory financing agreement	$	330.1	$	256.1
	Other inventory financing agreements	2		0.5
	Accounts payable-inventory financing	$	332.1	$	256.6
	As described in Note 7, in June 2014, the Company entered into a new senior secured asset-based revolving credit facility, which incorporates the previous inventory floorplan sub-facility and, among other changes, removes the $400.0 million limit on the size of the floorplan sub-facility. In connection with the floorplan sub-facility, the Company maintains an inventory financing agreement on an unsecured basis with a financial intermediary to facilitate the purchase of inventory from this vendor (the “Revolving Loan inventory financing agreement”). Amounts outstanding under the Revolving Loan inventory financing agreement are unsecured and non-interest bearing.
	The Company also maintains other inventory financing agreements with financial intermediaries to facilitate the purchase of inventory from certain vendors. At December 31, 2014 and 2013, amounts owed under other inventory financing agreements of $2.0 million and $0.5 million, respectively, were collateralized by the inventory purchased under these financing agreements and a second lien on the related accounts receivable.

Lease_Commitments

Lease Commitments	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Lease Commitments [Text Block]	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, 2014, 2013 and 2012, rent expense under these lease arrangements was $21.4 million, $20.7 million and $22.4 million, respectively.
	Future minimum lease payments are as follows:
	(in millions)
	Years ending December 31,
	2015	$	19.1
	2016	15.3
	2017	16.1
	2018	13.6
	2019	12.8
	Thereafter	50.6
	Total future minimum lease payments (1)	$	127.5
	(1) Included in these amounts are future minimum lease payments commencing in the fourth quarter of 2016 that relate to a new lease entered into in December 2014 for the Company’s future headquarters in Lincolnshire, Illinois. Also reflected in these amounts is the future expiration of two leases in the first quarter of 2016 for facilities currently in use by the Company which the Company plans to consolidate into the new headquarters location and accordingly, these leases will not be renewed.

LongTerm_Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt
	Long-term debt was as follows:
	(dollars in millions)				December 31,
		Interest Rate (1)			2014				2013
	Senior secured asset-based revolving credit facility	—	%		$	—			$	—
	Senior secured term loan facility	3.25	%		1,513.50				1,528.90
	Unamortized discount on senior secured term loan facility				(3.7		)		(4.4		)
	Senior secured notes due 2018	—	%		—				325
	Senior notes due 2019	8.5	%		503.9				1,305.00
	Unamortized premium on senior notes due 2019				1.3				4.2
	Senior notes due 2022	6	%		600				—
	Senior notes due 2024	5.5	%		575				—
	Senior subordinated notes due 2017	—	%		—				92.5
	Total long-term debt				3,190.00				3,251.20
	Less current maturities of long-term debt				(15.4		)		(45.4		)
	Long-term debt, excluding current maturities				$	3,174.60			$	3,205.80
	(1)Interest rate at December 31, 2014.
	At December 31, 2014, the Company was in compliance with the covenants under its various credit agreements and indentures as described below. Under the indenture governing the 8.5% Senior Notes due 2019, which contains the most restrictive restricted payment provisions in the Company’s various credit agreements and indentures, CDW LLC and its restricted subsidiaries are generally restricted from paying dividends and making other restricted payments. For the purpose of determining restricted payment capacity, consolidated net income or loss includes certain adjustments that are defined in the applicable indenture. At December 31, 2014, the amount of cumulative consolidated net income free of restrictions under the credit agreements and indentures ("Restricted Payment Capacity") was $230.3 million.
	Senior Secured Asset-Based Revolving Credit Facility (“Revolving Loan”)
	At December 31, 2014, the Company had no outstanding borrowings under the Revolving Loan, $2.1 million of undrawn letters of credit and $312.3 million reserved related to the floorplan sub-facility.
	On June 6, 2014, the Company entered into the Revolving Loan, a new five-year $1,250.0 million 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 for certain vendor products. The Revolving Loan matures on June 6, 2019, subject to an acceleration provision discussed below. The Revolving Loan replaces the Company’s previous revolving loan credit facility that was to mature on June 24, 2016. The Revolving Loan (i) increases the overall revolving credit facility capacity available to the Company from $900.0 million to $1,250.0 million, (ii) increases the maximum aggregate amount of increases that may be made to the revolving credit facility from $200.0 million to $300.0 million, (iii) maintains a maturity acceleration provision based upon excess cash availability whereby the Revolving Loan may mature 45 days prior to the final maturity of any then outstanding senior debt if excess cash availability does not exceed the outstanding borrowings of the subject maturing debt at the time of the test plus $150.0 million, (iv) decreases the fee on the unused portion of the revolving credit facility from either 37.5 or 50 basis points, depending on the amount of utilization, to 25 basis points, (v) decreases the applicable interest rate margin by 50 basis points, and (vi) amends the existing inventory floorplan sub-facility as discussed below. In connection with the termination of the previous facility, the Company recorded a loss on extinguishment of long-term debt of $0.4 million in the consolidated statement of operations for the year ended December 31, 2014, representing a write-off of a portion of unamortized deferred financing costs. Fees of $6.4 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.
	The Revolving Loan incorporates the previous inventory floorplan sub-facility and related Revolving Loan inventory financing agreement while removing the previous $400.0 million limit on the size of the floorplan sub-facility and the in-transit reserve of 15% of open orders. At December 31, 2014, the financial intermediary reported an outstanding balance of $312.3 million under the Revolving Loan inventory financing agreement. The amount included on the Company's consolidated balance sheet as of December 31, 2014 as accounts payable-inventory financing related to the Revolving Loan inventory financing agreement of $330.1 million includes a $17.8 million accrual for amounts in transit.
	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 (1.50% to 2.00% for LIBOR borrowings and 0.50% to 1.00% for ABR borrowings) depending upon average daily excess cash availability under the agreement evidencing the Revolving Loan and is subject to a reduction of 0.25% if, and for as long as, CDW LLC's corporate credit rating from Standard & Poor’s Rating Services is BB or better and CDW LLC's corporate family rating from Moody’s Investors Service, Inc. is Ba3 or better (in each case with stable or better outlook).
	Under the new Revolving Loan, the Company is permitted to borrow an aggregate amount of $1,250.0 million; however, its ability to borrow under the Revolving Loan is limited by a borrowing base. The borrowing base is (a) the sum of the products of the applicable advance rates on eligible accounts receivable and on eligible inventory as defined in the agreement less (b) any reserves. At December 31, 2014, the borrowing base was $1,253.4 million based on the amount of eligible inventory and accounts receivable balances as of November 30, 2014. The Company could have borrowed up to an additional $935.6 million under the Revolving Loan at December 31, 2014.
	The ability to borrow under the Revolving Loan also remains limited by a minimum liquidity condition which provides that, if excess cash availability is less than the lesser of (i) $125.0 million and (ii) the greater of (A) 10.0% of the borrowing base and (B) $100.0 million, the lenders are not required to lend any additional amounts under the Revolving Loan unless the consolidated fixed charge coverage ratio (as described in the agreement evidencing the Revolving Loan) is at least 1.00 to 1.00.
	CDW LLC is the borrower under the Revolving Loan. All obligations under the Revolving Loan are guaranteed by Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries. Borrowings under the Revolving Loan are collateralized by a first priority interest in inventory (excluding inventory collateralized under the inventory floorplan arrangements as described in Note 5), deposits, and accounts receivable, and a second priority interest in substantially all other assets. The Revolving Loan contains negative covenants that, among other things, place restrictions and limitations on the ability of Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries 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. The Revolving Loan also includes maintenance of a minimum average daily excess cash availability requirement. Should the Company fall below the minimum average daily excess cash availability requirement for five consecutive business days, the Company becomes subject to a fixed charge coverage ratio until such time as the daily excess cash availability requirement is met for 30 consecutive business days.
	Senior Secured Term Loan Facility
	On April 29, 2013, the Company entered into a seven-year, $1,350.0 million aggregate principal amount senior secured term loan facility (the "Term Loan"). The Term Loan was issued at a price that was 99.75% of par, which resulted in a discount of $3.4 million. Substantially all of the proceeds from the Term Loan were used to repay the $1,299.5 million outstanding aggregate principal amount of the prior senior secured term loan facility (the "Prior Term Loan Facility"). In connection with this refinancing, the Company recorded a loss on extinguishment of long-term debt of $10.3 million in the consolidated statement of operations for the year ended December 31, 2013. This loss represented a write-off of the remaining unamortized deferred financing costs related to the Prior Term Loan Facility.
	On July 31, 2013, the Company borrowed an additional $190.0 million aggregate principal amount under the Term Loan at a price that was 99.25% of par, which resulted in a discount of $1.4 million. Such proceeds were used to redeem a portion of outstanding Senior Subordinated Notes. The discounts are reported on the consolidated balance sheet as a reduction to the face amount of the Term Loan and are being amortized to interest expense over the term of the related debt. Fees of $6.1 million related to the Term Loan were capitalized as deferred financing costs and are being amortized over the term of the facility using the effective interest method.
	The Company is required to pay quarterly principal installments equal to 0.25% of the original principal amount of the Term Loan, with the remaining principal amount payable on the maturity date of April 29, 2020. The quarterly principal installment payments commenced during the quarter ended June 30, 2013. At December 31, 2014, the outstanding principal amount of the Term Loan was $1,513.5 million, excluding $3.7 million in unamortized discount.
	Borrowings under the Term Loan bear interest at either (a) the alternate base rate ("ABR") plus a margin or (b) LIBOR plus a margin; provided that for the purposes of the Term Loan, LIBOR shall not be less than 1.00% per annum at any time ("LIBOR Floor"). The margin is based upon a net leverage ratio as defined in the agreement governing the Term Loan, ranging from 1.25% to 1.50% for ABR borrowings and 2.25% to 2.50% for LIBOR borrowings. The total net leverage ratio was 3.1 at December 31, 2014. An interest rate of 3.25%, LIBOR Floor plus a 2.25% margin, was in effect during the three-month period ended December 31, 2014.
	In order to manage the risk associated with changes in interest rates on borrowings under the Term Loan, the Company has entered into interest rate cap agreements. The Company had ten interest rate cap agreements in effect through January 14, 2015 with a combined notional amount of $1,150.0 million which entitled the Company to payments from the counterparty of the amount, if any, by which three-month LIBOR exceeds a weighted average rate of 2.4% during the agreement period. The fair value of these interest rate cap agreements was zero at both December 31, 2014 and 2013.
	In connection with the expiration of the ten interest rate cap agreements noted above, during the year ended December 31, 2014, the Company entered into 14 additional interest rate cap agreements with a combined notional amount of $1,000.0 million. Under these agreements, the Company made premium payments totaling $2.1 million to the counterparties in exchange for the right to receive payments equal to the amount, if any, by which three-month LIBOR exceeds 2.0% during the agreement period. These interest rate cap agreements are effective from January 14, 2015 through January 14, 2017. The fair value of these interest rate cap agreements was $1.7 million at December 31, 2014.
	The Company's interest rate cap agreements have not been designated as cash flow hedges of interest rate risk for GAAP accounting purposes. The interest rate cap agreements are recorded at fair value on the Company’s consolidated balance sheet in Other Assets each period, with changes in fair value recorded directly to interest expense in the Company’s consolidated statements of operations. 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.
	See Note 20 for a description of the interest rate cap agreements entered into during the first quarter of 2015.
	On January 30, 2013, the Company made an optional prepayment of $40.0 million aggregate principal amount outstanding under the Prior Term Loan Facility. The optional prepayment satisfied the excess cash flow payment provision of the Prior Term Loan Facility with respect to the year ended December 31, 2012.
	CDW LLC is the borrower under the Term Loan. All obligations under the Term Loan are guaranteed by Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries. 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 5), deposits, and accounts receivable, and by a first priority interest in substantially all other assets. The Term Loan contains negative covenants that, among other things, place restrictions and limitations on the ability of Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries 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.
	8.0% Senior Secured Notes due 2018 (“Senior Secured Notes”)
	At December 31, 2014, there were no outstanding Senior Secured Notes.
	On August 5, 2014, the proceeds from the issuance of the 2022 Senior Notes discussed below, along with cash on hand, were deposited with the trustee to redeem all of the remaining $325.0 million aggregate principal amount of the Senior Secured Notes at a redemption price of 106.061% of the principal amount redeemed, plus accrued and unpaid interest through the date of redemption. On the same date, the indenture governing the Senior Secured Notes was satisfied and discharged. The redemption date was September 5, 2014. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $23.7 million in the consolidated statement of operations for the year ended December 31, 2014, which was comprised of $4.0 million for the write-off of the unamortized deferred financing fees, a redemption premium of $13.0 million and a make-whole interest payment of $6.7 million.
	On July 2, 2013, the Company used a portion of the net proceeds from the IPO to redeem $175.0 million aggregate principal amount of Senior Secured Notes. The redemption price of the Senior Secured Notes was 108.0% of the principal amount redeemed, plus $0.7 million of accrued and unpaid interest to the date of redemption. The Company used cash on hand to pay such accrued and unpaid interest. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $16.7 million in the consolidated statement of operations for the year ended December 31, 2013. This loss represented $14.0 million in redemption premium and $2.7 million for the write-off of a portion of the remaining deferred financing costs related to the Senior Secured Notes.
	8.5% Senior Notes due 2019 (“2019 Senior Notes”)
	At December 31, 2014, the outstanding principal amount of 2019 Senior Notes was $503.9 million, excluding $1.3 million in unamortized premium. The 2019 Senior Notes mature on April 1, 2019.
	On December 1, 2014, the proceeds from the issuance of the 2024 Senior Notes discussed below, along with cash on hand, were deposited with the trustee to redeem $541.4 million aggregate principal amount of the 2019 Senior Notes at a redemption price of 106.202% of the principal amount redeemed, plus accrued and unpaid interest through the date of redemption. The redemption date was December 31, 2014. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $36.9 million in the consolidated statement of operations for the year ended December 31, 2014, which was comprised of $4.7 million for the write-off of a portion of the unamortized deferred financing fees, a redemption premium of $23.0 million, and a make-whole interest payment of $10.6 million, partially offset by $1.4 million for the write-off of a portion of the unamortized premium.
	On August 5, 2014, the proceeds from the issuance of the 2022 Senior Notes discussed below, along with cash on hand, were deposited with the trustee to redeem $234.7 million aggregate principal amount of the 2019 Senior Notes at a redemption price of 108.764% of the principal amount redeemed, plus accrued and unpaid interest through the date of redemption. The redemption date was September 5, 2014. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $22.1 million in the consolidated statement of operations for the year ended December 31, 2014, which was comprised of $2.2 million for the write-off of a portion of the unamortized deferred financing fees, a redemption premium of $10.0 million, and a make-whole interest payment of $10.6 million, partially offset by $0.7 million for the write-off of a portion of the unamortized premium.
	On March 20, 2014, the Company repurchased and subsequently canceled $25.0 million aggregate principal amount of the 2019 Senior Notes from an affiliate of Providence Equity in a privately negotiated transaction on an arms' length basis at a price of 109.75% of the principal amount. Cash on hand was used to fund the repurchase of $25.0 million aggregate principal amount, $2.4 million of repurchase premium and $1.0 million in accrued and unpaid interest to the date of repurchase. In connection with this repurchase, the Company recorded a loss on extinguishment of long-term debt of $2.7 million in the Company's consolidated statement of operations for the year ended December 31, 2014. This loss represented $2.4 million in repurchase premium and $0.3 million for the write-off of a portion of the unamortized deferred financing costs related to the 2019 Senior Notes.
	CDW LLC and CDW Finance Corporation are the co-issuers of the 2019 Senior Notes. Obligations under the 2019 Senior Notes are guaranteed on an unsecured senior basis by Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries. The 2019 Senior Note indenture contains negative covenants that, among other things, place restrictions and limitations on the ability of Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries 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. The 2019 Senior Notes do not contain any financial covenants.
	6.0% Senior Notes due 2022 ("2022 Senior Notes")
	On August 5, 2014, CDW LLC and CDW Finance Corporation, as co-issuers, completed the issuance of $600.0 million aggregate principal amount of 2022 Senior Notes at par. Fees of $8.0 million related to the 2022 Senior Notes were capitalized as deferred financing costs and are being amortized over the term of the notes on a straight-line basis. The 2022 Senior Notes will mature on August 15, 2022 and bear interest at a rate of 6.00% per annum, payable semi-annually on February 15 and August 15 of each year. The first interest payment date was February 15, 2015.
	CDW LLC and CDW Finance Corporation are the co-issuers of the 2022 Senior Notes and the obligations under the notes are guaranteed by Parent and each of CDW LLC's direct and indirect, wholly owned, domestic subsidiaries. The 2022 Senior Notes indenture contains negative covenants that, among other things, place restrictions and limitations on the ability of Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries to enter into sale and lease-back transactions, incur additional secured indebtedness, and create liens. The indenture governing the 2022 Senior Notes does not contain any financial covenants.
	5.5% Senior Notes due 2024 ("2024 Senior Notes")
	On December 1, 2014, CDW LLC and CDW Finance Corporation, as co-issuers, completed the issuance of $575.0 million aggregate principal amount of 2024 Senior Notes at par. Fees of $7.5 million related to the 2024 Senior Notes were capitalized as deferred financing costs and are being amortized over the term of the notes on a straight-line basis. The 2024 Senior Notes will mature on December 1, 2024 and bear interest at a rate of 5.50% per annum, payable semi-annually on June 1 and December 1 of each year. The first interest payment date will be June 1, 2015.
	CDW LLC and CDW Finance Corporation are the co-issuers of the 2024 Senior Notes and the obligations under the notes are guaranteed by Parent and each of CDW LLC's direct and indirect, wholly owned, domestic subsidiaries. The 2024 Senior Notes indenture contains negative covenants that, among other things, place restrictions and limitations on the ability of Parent and each of CDW LLC's direct and indirect, 100% owned, domestic subsidiaries to enter into sale and lease-back transactions, incur additional secured indebtedness, and create liens. The indenture governing the 2024 Senior Notes does not contain any financial covenants.
	12.535% Senior Subordinated Exchange Notes due 2017 (“Senior Subordinated Notes”)
	At December 31, 2014, there were no outstanding Senior Subordinated Notes.
	On May 9, 2014, the Company redeemed all of the remaining $42.5 million aggregate principal amount of Senior Subordinated Notes at a redemption price that was 104.178% of the principal amount redeemed. Cash on hand was used to fund the redemption of $42.5 million aggregate principal amount, $1.8 million in redemption premium and $0.4 million in accrued and unpaid interest to the date of redemption. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $2.2 million in the consolidated statement of operations for the year ended December 31, 2014. This loss represented $1.8 million in redemption premium and $0.4 million for the write-off of the remaining deferred financing costs related to the Senior Subordinated Notes.
	On January 22, 2014 and February 21, 2014, the Company redeemed $30.0 million and $20.0 million aggregate principal amounts of Senior Subordinated Notes, respectively, at redemption prices that were 104.178% of the principal amounts redeemed. Cash on hand was used to fund the redemptions of $50.0 million aggregate principal amount, $2.1 million in redemption premiums and $1.9 million in aggregate accrued and unpaid interest to the dates of redemption. In connection with these redemptions, the Company recorded a loss on extinguishment of long-term debt of $2.7 million in the consolidated statement of operations for the year ended December 31, 2014. This loss represented $2.1 million in redemption premiums and $0.6 million for the write-off of a portion of the remaining deferred financing costs related to the Senior Subordinated Notes.
	On October 18, 2013, the Company redeemed $155.0 million aggregate principal amount of Senior Subordinated Notes at a redemption price that was 104.178% of the principal amount redeemed. A combination of cash on hand and the net proceeds from the sale of shares of common stock related to the underwriters' exercise in full of the overallotment option granted to them in connection with the IPO, in the amount of $56.0 million, was used to fund the redemption of $155.0 million aggregate principal amount, $6.5 million of redemption premium and $0.2 million in accrued and unpaid interest to the date of redemption. See Note 9 for additional discussion of the underwriters' overallotment option. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $8.5 million in the Company's consolidated statement of operations for the year ended December 31, 2013. This loss represented $6.5 million in redemption premium and $2.0 million for the write-off of a portion of the remaining unamortized deferred financing costs related to the Senior Subordinated Notes.
	On August 1, 2013, the Company redeemed $324.0 million aggregate principal amount of Senior Subordinated Notes at a redemption price that was 106.268% of the principal amount redeemed. The Company used a portion of the net proceeds from the IPO to redeem $146.0 million aggregate principal amount of Senior Subordinated Notes and incremental borrowings of $190.0 million under the Term Loan to redeem $178.0 million aggregate principal amount of Senior Subordinated Notes. The Company used cash on hand to pay $12.0 million of accrued and unpaid interest to the date of redemption. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $24.6 million in the consolidated statement of operations for the year ended December 31, 2013. This loss represented $20.3 million in redemption premium and $4.3 million for the write-off of a portion of the remaining deferred financing costs related to the Senior Subordinated Notes.
	On March 8, 2013, the Company redeemed $50.0 million aggregate principal amount of Senior Subordinated Notes at a redemption price that was 106.268% of the principal amount redeemed. Cash on hand was used to fund the redemption of $50.0 million aggregate principal amount, $3.1 million of redemption premium and $2.5 million in accrued and unpaid interest to the date of redemption. In connection with this redemption, the Company recorded a loss on extinguishment of long-term debt of $3.9 million in the Company's consolidated statement of operations for the year ended December 31, 2013. This loss represented $3.1 million in redemption premium and $0.8 million for the write-off of a portion of the remaining unamortized deferred financing costs related to the Senior Subordinated Notes.
	Long-Term Debt Maturities
	As of December 31, 2014, the maturities of long-term debt were as follows:
	(in millions)
	Years ending December 31,
2015	$	15.4
2016	—
2017	—
2018	—
2019	503.9
Thereafter	2,673.10
	$	3,192.40
Fair Value
The fair value of the Company's long-term debt instruments at December 31, 2014 was $3,208.7 million. The fair value of the 2019 Senior Notes, the 2022 Senior Notes, and the 2024 Senior Notes was estimated using quoted market prices for identical assets or 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 assets or liabilities in markets that are not considered active. Consequently, the Company's long-term debt is classified as Level 2 within the fair value hierarchy.
At December 31, 2014, the carrying value of the Company's long-term debt was $3,192.4 million, excluding $1.3 million in unamortized premium and $3.7 million in unamortized discount.
Deferred Financing Costs
The following table summarizes the deferred financing costs activity for the years ended December 31, 2014 and 2013:
(in millions)	December 31,
	2014				2013
Beginning balance	$	30.1			$	53.2
Additional costs capitalized	21.9				6.1
Recognized in interest expense	(6.4		)		(9.1		)
Write-off of unamortized deferred financing costs	(12.6		)		(20.1		)
Ending balance	$	33			$	30.1
As of December 31, 2014 and December 31, 2013, the weighted-average remaining life of unamortized deferred financing costs was 6.6 and 4.9 years, respectively.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	Income before income taxes was taxed under the following jurisdictions:
	(in millions)	Years Ended December 31,
		2014			2013				2012
	Domestic	$	366.6		$	179.4			$	170.3
	Foreign	21.1			16.1				15.8
	Total	$	387.7		$	195.5			$	186.1
	Components of income tax expense (benefit) consisted of the following:
	(in millions)	Years Ended December 31,
		2014			2013				2012
	Current:
	Federal	$	206.8		$	96.7			$	110.3
	State	19.3			10.1				8
	Foreign	5.8			4.6				5.1
	Total current	231.9			111.4				123.4
	Deferred:
	Domestic	(89.0		)	(48.6		)		(56.2		)
	Foreign	(0.1		)	(0.1		)		(0.1		)
	Total deferred	(89.1		)	(48.7		)		(56.3		)
	Income tax expense	$	142.8		$	62.7			$	67.1
	The reconciliation between the statutory tax rate expressed as a percentage of income before income taxes and the effective tax rate is as follows:
	(dollars in millions)	Years Ended December 31,
		2014						2013						2012
	Statutory federal income tax rate	$	135.7		35	%		$	68.4			35	%	$	65.1		35	%
	State taxes, net of federal effect	6.5			1.6			(5.0		)		(2.6	)	0.4			0.2
	Equity-based compensation	1.1			0.3			1.5				0.7		5.7			3.1
	Effect of rates different than statutory	(1.9		)	(0.5	)		(1.4		)		(0.7	)	(1.4		)	(0.8	)
	Other	1.4			0.4			(0.8		)		(0.3	)	(2.7		)	(1.5	)
	Effective tax rate	$	142.8		36.8	%		$	62.7			32.1	%	$	67.1		36	%
	The tax effect of temporary differences that give rise to the net deferred income tax liability is presented below:
	(in millions)	December 31,
		2014			2013
	Deferred Tax Assets:
	Deferred interest	$	32.9		$	43.5
	State net operating loss and credit carryforwards, net	18.8			21.1
	Payroll and benefits	27			16.2
	Rent	5.5			6.4
	Accounts receivable	6.3			5.4
	Equity compensation plans	6.5			1.6
	Trade credits	1.5			1.5
	Other	5			7.1
	Total deferred tax assets	103.5			102.8
	Deferred Tax Liabilities:
	Software and intangibles	425.3			486.2
	Deferred income	116.2			145.5
	Property and equipment	22.5			25
	Other	15.3			11.6
	Total deferred tax liabilities	579.3			668.3
	Deferred tax asset valuation allowance	—			—
	Net deferred tax liability	$	475.8		$	565.5
	The Company has state income tax net operating loss carryforwards of $124.0 million, which will expire at various dates from 2015 through 2033 and state tax credit carryforwards of $19.6 million, which expire at various dates from 2016 through 2019.
	The Company has not provided for U.S. federal income taxes or tax benefits on the undistributed earnings of its international subsidiary because such earnings are reinvested and it is currently intended that they will continue to be reinvested indefinitely. At December 31, 2014, the Company has not provided for federal income taxes on earnings of approximately $66.6 million from its international subsidiary.
	The Company had no unrecognized tax benefits at December 31, 2014, 2013 and 2012.
	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 2010 and state, local or foreign taxing authorities for tax years through 2009. 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.
	The Company accrues net interest and penalties related to unrecognized tax benefits in income tax expense in its consolidated statements of operations. For the years ended December 31, 2014, 2013 and 2012, the Company had no liability recorded for the payment of interest and penalties on unrecognized tax benefits and did not recognize any such interest and penalty expense.

Shareholders_Equity_Notes

Shareholders' Equity (Notes)	12 Months Ended
	Dec. 31, 2014
Shareholders' Equity [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	Shareholders' Equity
	The Company declared and paid cash dividends per common share during the periods presented as follows:
	(in millions, except per share amounts)		Dividends Per Share			Amount
	2014:00:00
	First Quarter		$	0.0425		$	7.3
	Second Quarter		0.0425			7.3
	Third Quarter		0.0425			7.3
	Fourth Quarter		0.0675			11.7
	2013:00:00
	First Quarter		$	—		$	—
	Second Quarter		—			—
	Third Quarter		—			—
	Fourth Quarter		0.0425			7.3
	See Note 20 for a discussion of the dividend declared during the first quarter of 2015. Future dividends will be subject to the approval of the Company's Board of Directors and will depend upon the Company’s results of operations, financial condition, business prospects, capital requirements, contractual restrictions, any potential indebtedness the Company may incur, restrictions imposed by applicable law, tax considerations and other factors that the Company’s Board of Directors deems relevant. In addition, the Company’s ability to pay dividends on its common stock will be limited by restrictions on the ability of subsidiaries to pay dividends or make distributions to the Company, in each case, under the terms of certain current and future agreements governing the Company’s indebtedness.
	On November 6, 2014, the Company announced that its Board of Directors approved a $500.0 million share repurchase program effective immediately under which the Company may repurchase shares of its common stock in the open market or through privately negotiated 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. As of the date of this filing, no shares have been repurchased under the share repurchase program.
	On January 1, 2014, the first offering period under the Company's Coworker Stock Purchase Plan (the “CSPP”) commenced. The CSPP 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.
	On July 2, 2013, the Company completed an IPO of 23,250,000 shares of common stock. On July 31, 2013, the Company completed the sale of an additional 3,487,500 shares of common stock to the underwriters of the IPO pursuant to the underwriters' July 26, 2013 exercise in full of the overallotment option granted to them in connection with the IPO. Such shares were registered under the Securities Act of 1933, as amended, pursuant to the Company's Registration Statement on Form S-1, which was declared effective by the SEC on June 26, 2013. The shares of common stock are listed on the NASDAQ Global Select Market under the symbol “CDW.” The Company's shares of common stock were sold to the underwriters at a price of $17.00 per share in the IPO and upon the exercise of the overallotment option, which together generated aggregate net proceeds of $424.7 million to the Company after deducting underwriting discounts, expenses and transaction costs.
	The Company has completed the following secondary public offerings, whereby certain selling stockholders sold shares of common stock to the underwriters. The Company did not receive any proceeds from these sales of shares.
	Secondary Offering Shares			Completion Date of Secondary Offering	Overallotment Shares (1)		Completion Date of Overallotment Shares	Secondary Offering Expenses
								(in millions)
	15,000,000			11/19/13	2,250,000		12/18/13	$	0.6
	10,000,000			3/12/14	1,500,000		3/12/14	$	0.4
	15,000,000			5/28/14	2,250,000		6/4/14	$	0.5
	15,000,000			9/8/2014 (2)	—		—	$	0.3
	15,000,000			12/8/14	2,250,000		12/8/14	$	0.2
	(1) Under each underwriting agreement, the selling stockholders granted the underwriters an option, exercisable for thirty days, to purchase up to the additional amount of shares noted.
	(2) The option to purchase additional shares was not exercised in connection with the September 2014 secondary offering.
	The following pre-tax IPO-related expenses and secondary-offering-related expenses were included within selling and administrative expenses in the consolidated statements of operations for the years ended December 31, 2014 and 2013, respectively.
	(in millions)	Year Ended December 31,
		2014			2013
	Acceleration charge for certain equity awards and related employer payroll taxes(1)	$	—		$	40.7
	RDU Plan cash retention pool accrual(2)	—			7.5
	Management services agreement termination fee(3)	—			24.4
	Other expenses (4)	1.4			2.4
	IPO- and secondary-offering-related expenses	$	1.4		$	75
	(1) See Note 10 for additional discussion of the impact of the IPO on the Company's equity awards.
	(2) See Note 12 for additional discussion of this transaction.
	(3) Represents the payment of a termination fee to affiliates of the Sponsors in connection with the termination of the management services agreement with such entities.
	(4) Other expenses include secondary-offering expenses of $1.4 million and $0.6 million for the years ended December 31, 2014 and 2013, respectively.
	In June 2013, the Company’s Board of Directors and the Company's sole shareholder at that time, CDW Holdings, approved the reclassification of the Company’s Class A common shares and Class B common shares into a single class of common shares and a 143.0299613-for-1 stock split, effective immediately. The par value of the common shares was maintained at $0.01 per share. All references to common shares and per share amounts in the accompanying consolidated financial statements have been adjusted to reflect the reclassification and stock split on a retroactive basis.
	In June 2013, the Company amended and restated its certificate of incorporation to authorize the issuance of 100,000,000 shares of preferred stock with a par value of $0.01. No shares of preferred stock have been issued or are outstanding as of December 31, 2014. Additionally, the amended and restated certificate of incorporation increased the number of authorized common shares to 1,000,000,000.

EquityBased_Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-Based Compensation	Equity-Based Compensation
	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 11,700,000 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 discussed below. As of December 31, 2014, 7,541,891 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.
	The following table summarizes equity-based compensation expense, which is included in selling and administrative expenses, for the years ended December 31, 2014, 2013 and 2012:
	(in millions)		Year Ended December 31,
			2014				2013 (1)			2012 (2)
	Equity-based compensation expense		$	16.4			$	46.6		$	22.1
	Income tax benefit		(5.1		)		(16.5		)	(2.3		)
	Total (net of tax)		$	11.3			$	30.1		$	19.8
	-1	Includes pre-tax expense of $36.7 million related to the accelerated vesting of certain equity awards granted prior to our IPO. All unvested awards granted pursuant to the MPK Coworker Incentive Plan II (the “MPK Plan”) vested in connection with the IPO as discussed further below in the section labeled "MPK II Units."
	-2	Includes pre-tax expense of $6.6 million in connection with the modification of Class B Common Unit awards granted pursuant to the CDW Holdings LLC 2007 Incentive Equity Plan to the Company’s former Chief Executive Officer, as discussed further below in the section labeled "Class B Common Units."
	The total unrecognized compensation cost related to nonvested awards was $28.9 million at December 31, 2014 and is expected to be recognized over a weighted-average period of 2.3 years.
	Stock Options
	During the year ended December 31, 2014, the Company granted 1,245,513 stock options under the 2013 LTIP. These options vest annually over three years and have a contractual term of 10 years. The exercise price of a stock option is equal to the fair value of a share of the Company's common stock on the date of the grant. The Company uses the Black-Scholes option pricing model to estimate the fair value of stock options granted. The Black-Scholes option pricing model incorporates various assumptions including volatility, expected term, risk-free interest rates and dividend yields. The weighted-average assumptions used to value the stock options granted during the years ended December 31, 2014 and 2013 are presented below.
			Year Ended December 31,
			2014				2013
	Weighted-average grant date fair value		$	7.23			$	4.75
	Weighted-average volatility (1)		30		%		35		%
	Weighted-average risk-free rate (2)		1.77		%		1.58		%
	Dividend yield		0.7		%		1		%
	Expected term (in years) (3)		6				5.4
	-1	Based upon an assessment of the two-year, five-year and implied volatility for the Company’s selected peer group, adjusted for the Company’s leverage.
	-2	Based on a composite U.S. Treasury rate.
	-3	Calculated using the simplified method. The simplified method 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.
	The following table summarizes the Company's stock option activity for the year ended December 31, 2014:
	Options		Number of Options			Weighted-Average Exercise Price			Weighted-Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (millions)
	Outstanding at January 1, 2014		1,280,255			$17.00
	Granted		1,245,513			24.4
	Forfeited/Expired		(31,209	)		21.33
	Exercised		(73,487	)		17
	Outstanding at December 31, 2014		2,421,072			$20.75			8.3	$34.90
	Exercisable at December 31, 2014		576,963			$17.00			7.2	$10.50
	Vested and expected to vest at December 31, 2014		2,378,364			$20.74			8.3	$34.30
	The total intrinsic value of stock options exercised during the years ended December 31, 2014 and 2013 was $1.0 million and zero, 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 following table summarizes the Company's RSU activity for the year ended December 31, 2014:
		Number of Units			Weighted-Average Grant-Date Fair Value
	Nonvested at January 1, 2014	1,351,572			$	17.04
	Granted	25,895			24.29
	Vested/Settled	(5,984	)		17
	Forfeited	(126,781	)		17.04
	Nonvested at December 31, 2014	1,244,702			$	17.19
	The weighted-average grant date fair value of RSUs granted during the year ended December 31, 2014 and 2013 was $24.29 and $17.03, respectively. The aggregate fair value of RSUs that vested during the years ended December 31, 2014 and 2013, was $0.2 million and zero, respectively.
	Performance Share Units ("PSUs")
	During the year ended December 31, 2014, the Company granted 417,784 PSUs under the 2013 LTIP which cliff-vest on December 31, 2016. The percentage of shares 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. The weighted-average grant-date fair value of the PSUs granted during the period was $24.40 per unit. During the year ended December 31, 2014, 6,204 PSUs were forfeited at a weighted-average grant-date fair value of $24.29. As of December 31, 2014, 411,580 PSUs were outstanding at a weighted-average grant date fair value of $24.40. No units vested during the year ended December 31, 2014.
	Restricted Stock
	In connection with the IPO, CDW Holdings distributed all of its shares of the Company's common stock to its existing members in accordance with their respective membership interests. Common stock received by holders of Class B Common Units in connection with the distribution is subject to any vesting provisions previously applicable to the holder's Class B Common Units. 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 distribution. For the year ended December 31, 2014, 2,321,973 shares of such restricted stock vested/settled and 9,546 shares were forfeited. As of December 31, 2014, 260,514 shares of restricted stock were outstanding. The aggregate fair value of restricted stock that vested during the years ended December 31, 2014 and 2013 was $68.6 million and $26.7 million, respectively.
	Pre-IPO Equity Awards
	Prior to the IPO, the Company had the following equity-based compensation plans in place:
	Class B Common Units
	The Board of Managers of CDW Holdings adopted the CDW Holdings LLC 2007 Incentive Equity Plan (the “Plan”) for coworkers, managers, consultants and advisors of the Company and its subsidiaries. The Plan permitted a committee designated by the Board of Managers of CDW Holdings (the “Committee”) to grant or sell to any participant Class A Common Units or Class B Common Units of CDW Holdings in such quantity, at such price, on such terms and subject to such conditions that were consistent with the Plan and as established by the Committee.
	The Class B Common Units that were granted vested daily on a pro rata basis between the date of grant and the fifth anniversary thereof and were subject to repurchase by, with respect to vested units, or forfeiture to, with respect to unvested units, the Company upon the coworker's separation from service as was set forth in each holder’s Class B Common Unit Grant Agreement.
	On June 30, 2011, the Board of Managers approved the terms of a modified Class B Common Unit grant agreement with the Company's former Chief Executive Officer, who retired as the Company's Chief Executive Officer effective October 1, 2011 but continued to serve as Chairman of the Board through December 31, 2012. As a result of this modification, the Company recorded incremental equity-based compensation expense of $6.6 million during the year ended December 31, 2012.
	The grant date fair value of Class B Common Unit grants was calculated using the Option-Pricing Method. This method considered Class A Common Units and Class B Common Units as call options on the total equity value, giving consideration to liquidation preferences and conversion of the preferred units. Such Class A Common Units and Class B Common Units were modeled as call options that gave their owners the right, but not the obligation, to buy the underlying equity value at a predetermined (or exercise) price. Class B Common Units were considered to be call options with a claim on equity value at an exercise price equal to the remaining value immediately after the Class A Common Units and Class B Common Units with a lower participation threshold were liquidated. The Option-Pricing Method is highly sensitive to key assumptions, such as the volatility assumption. As such, the use of this method can be applied when the range of possible future outcomes is difficult to predict.
	The following table summarizes the assumptions and resulting fair value of the Class B Common Unit grants for the years ended December 31, 2013 and 2012:
		Years Ended December 31,
	Assumptions	2013				2012
	Weighted-average grant date fair value	$	119			$	125.65
	Weighted-average volatility (1)	65.5		%		65.26		%
	Weighted-average risk-free rate (2)	0.18		%		0.19		%
	Dividend yield	0		%		0		%
	-1	Based upon an assessment of the two-year, five-year and implied volatility for the Company’s selected peer group, adjusted for the Company’s leverage.
	-2	Based on a composite U.S. Treasury rate.
	MPK II Units
Contemporaneous with the Acquisition, the Company agreed with Michael P. Krasny, CDW Corporation founder, former chairman and CEO and significant selling shareholder, to establish the MPK Plan for the benefit of all of the coworkers of the Company other than members of senior management who received incentive equity awards under the Plan.
The MPK Plan established an “account” for each eligible participant which was notionally credited with a number of Class A Common Units of CDW Holdings LLC on October 15, 2007, the day the plan was established. The notional units credited to participants' accounts were to cliff-vest at the end of ten years, subject to acceleration upon the occurrence of certain events. Notional units granted under the MPK Plan were valued on the grant date at $1,000 per unit, the fair value equivalent of the Class A Common Units at the time the awards were granted.
On July 2, 2013, the Company completed an IPO of its common shares. Under the terms of the MPK Plan, vesting accelerated for all unvested units upon completion of the IPO. The Company recorded a pre-tax charge of $36.7 million for compensation expense related to the acceleration of the expense recognition for MPK Plan units in the year ended December 31, 2013. In connection with the completion of the IPO, the Company distributed common stock to each participant and withheld the number of shares of common stock equal to the required tax withholding for each participant. The Company paid required withholding taxes of $24.0 million to federal, state and foreign taxing authorities. This amount is reported as a financing activity in the consolidated statement of cash flows and as an increase to accumulated deficit in the consolidated statement of shareholders' equity for the year ended December 31, 2013. In addition, the Company paid $4.0 million of employer payroll taxes that are included as an operating activity in the consolidated statement of cash flows for the year ended December 31, 2013.
The following table sets forth a summary of pre-IPO equity plan activity for the year ended December 31, 2013:
	Class B			MPK Plan
	Common Units			Units
Outstanding at January 1, 2013	216,483			66,137
Granted	400			—
Forfeited	(860	)		(2,228	)
Converted/Settled (1)	(216,023	)		(63,909	)
Outstanding at December 31, 2013	—			—
Vested at December 31, 2013	—			—
-1	As discussed above, the Class B Common Units and MPK Plan Units were converted/settled into shares of the Company's common stock upon completion of the IPO. The converted Class B Common Units, to the extent unvested at the time of the IPO, relate to the grants of restricted stock disclosed above.
In connection with the establishment of the MPK Plan, the Company agreed to make charitable contributions in amounts equal to the net income tax benefits derived from payouts to participants under the MPK Plan (net of any related employer payroll tax costs). The contributions of these amounts are due by March 15 of the calendar year following the year in which the Company realizes the benefits of the deductions. This arrangement has been accounted for as contingent consideration. Pre-2009 business combinations were accounted for under a former accounting standard which, among other aspects, precluded the recognition of certain contingent consideration as of the business combination date. Instead, under the former accounting standard, contingent consideration is accounted for as additional purchase price (goodwill) at the time the contingency is resolved. As of December 31, 2013, the Company accrued $20.9 million related to this arrangement within other current liabilities, as the Company realized the tax benefit of the compensation deductions during the 2013 tax year. The Company made the related cash contribution during the first quarter of 2014.

Earnings_per_Share_Notes

Earnings per Share (Notes)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	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 number of common shares outstanding during the period. The 2013 denominator was impacted by the common shares issued during both the IPO and the underwriters' exercise in full of the overallotment option granted to them in connection with the IPO. Because such common shares were issued on July 2, 2013 and July 31, 2013, respectively, they are only partially reflected in the 2013 denominator. Such shares are fully reflected in the 2014 denominator. See Note 9 for additional discussion of the IPO.
	The dilutive effect of outstanding restricted stock, restricted stock units, stock options, Coworker Stock Purchase Plan units and MPK Plan units is reflected in the denominator for diluted earnings per share using the treasury stock method.
	The following is a reconciliation of basic shares to diluted shares:
		Years Ended December 31,
	(in millions)	2014	2013	2012
	Weighted-average shares - basic	170.6	156.6	145.1
	Effect of dilutive securities	2.2	2.1	0.7
	Weighted-average shares - diluted	172.8	158.7	145.8
	There was an insignificant amount of potential common shares excluded from diluted earnings per share for the years ended December 31, 2014, 2013 and 2012, as their inclusion would have had an anti-dilutive effect.

Deferred_Compensation_Plan

Deferred Compensation Plan	12 Months Ended
	Dec. 31, 2014
Deferred Compensation Arrangements [Abstract]
Deferred Compensation Plan	Deferred Compensation Plan
	On March 10, 2010, in connection with the Company’s purchase of $28.5 million principal amount of its outstanding senior subordinated debt, the Company established the Restricted Debt Unit Plan (the “RDU Plan”), an unfunded nonqualified deferred compensation plan. The total number of RDUs that could be granted under the RDU Plan was 28,500. As of December 31, 2014, 28,500 RDUs were outstanding. RDUs vested daily on a pro rata basis over the three-year period from January 1, 2012 (or, if later, the date of hire or the date of a subsequent RDU grant) through December 31, 2014. All outstanding RDUs were vested as of December 31, 2014. Participants have no rights to the underlying debt.
	The total amount of compensation available to be paid under the RDU Plan was initially to be based on two components, a principal component and an interest component. The principal component credits the RDU Plan with a notional amount equal to the $28.5 million face value of the Senior Subordinated Notes (the "Debt Pool"), together with certain redemption premium equivalents as noted below. The interest component credited the RDU Plan with amounts equal to the interest that would have been earned on the Debt Pool from March 10, 2010 through maturity on October 12, 2017, except as discussed below. Interest amounts for 2010 and 2011 were deferred until 2012, and thereafter, interest amounts were paid to participants semi-annually on the interest payment due dates.
	The Company used a portion of the IPO proceeds together with incremental borrowings to redeem $324.0 million of the total Senior Subordinated Notes outstanding on August 1, 2013. In connection with the IPO and the partial redemption of the Senior Subordinated Notes, the Company amended the RDU Plan to increase the retentive value of the plan. In accordance with the original terms of the RDU Plan, the principal component of the RDUs converted to a cash-denominated pool upon the redemption of the Senior Subordinated Notes. In addition, the Company added $0.1 million and $1.4 million to the principal component in the years ended December 31, 2014 and 2013, respectively, as redemption premium equivalents in accordance with the terms of the RDU plan.
	Under the terms of the amended RDU Plan, upon the partial redemption of outstanding Senior Subordinated Notes, the RDUs ceased to accrue the proportionate related interest component credits. The amended RDU Plan provides participants the opportunity to share on a pro rata basis in cash retention pools payable to participants who satisfy certain retention requirements. The aggregate amount of the retention pools was determined to be $15.0 million based upon the amount of interest component credits that would have been allocated to the RDU Plan if the Senior Subordinated Notes had remained outstanding from August 1, 2013 through maturity. The Company recorded a pre-tax charge of $7.5 million in the year ended December 31, 2013 for payment of the first cash retention pool. The second cash retention pool payment is expected to be made to participants who remain employed through December 31, 2015 in the first quarter of 2016. Participants continued to accrue an interest component credit for the proportionate amount of Senior Subordinated Notes while outstanding, payable on the aforementioned semi-annual due dates; such payments, however, will be deducted from the second retention pool payment amount of $7.5 million.
	Unrecognized compensation expense as of December 31, 2014 of approximately $5 million is expected to be recognized through 2015 and approximately $3 million in 2016 through 2017. Payments under the RDU Plan may be impacted if certain significant events occur or circumstances change that would impact the financial condition or structure of the Company.
	Compensation expense of $8.8 million, $16.8 million, and $8.4 million related to the RDU Plan was recognized in the years ended December 31, 2014, 2013 and 2012, respectively. At December 31, 2014 and 2013, the Company had $30.4 million and $21.8 million of liabilities related to the RDU Plan recorded on the consolidated balance sheets, respectively.
	Payment of the principal component of the RDU Plan is expected to be made on October 12, 2017, unless accelerated due to a sale of the Company.

Profit_Sharing_And_401K_Plan

Profit Sharing And 401(K) Plan	12 Months Ended
	Dec. 31, 2014
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Profit Sharing And 401(K) Plan	Profit Sharing and 401(k) Plan
	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. Company contributions to the profit sharing plan are made in cash and determined at the discretion of the Board of Directors. For the years ended December 31, 2014, 2013 and 2012, the amounts charged to expense for this plan totaled $21.9 million, $17.3 million and $14.6 million, respectively.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Loss Contingency [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 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 U.S. bankruptcy laws. 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, 2014, 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.

Equity_Investments_Notes

Equity Investments (Notes)	12 Months Ended
	Dec. 31, 2014
Equity Investments [Abstract]
Equity Method Investments and Joint Ventures Disclosure [Text Block]
	15	Equity Investments
	On November 10, 2014, the Company acquired a 35% non-controlling interest in Kelway, a UK-based IT solutions provider, which has global supply chain relationships that enable it to conduct business in over 100 countries. The Company paid $86.8 million to acquire its ownership interest in Kelway, with the option to purchase the remaining 65% between June 2015 and June 2017. The Company accounts for its investment in Kelway using the equity method. As of December 31, 2014, the amount assigned to goodwill and definite-lived intangible assets related to the Company's 35% non-controlling equity investment in Kelway was $119.2 million, which represented the excess of the purchase price plus liabilities assumed less tangible assets acquired.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions
	The Company had previously entered into a management services agreement with the Sponsors pursuant to which they had agreed to provide it with management and consulting services and financial and other advisory services. Pursuant to such agreement, the Sponsors received an annual management fee of $5.0 million and reimbursement of out-of-pocket expenses incurred in connection with the provision of such services. Such amounts were classified as selling and administrative expenses within the consolidated statements of operations. The management services agreement included customary indemnification and provisions in favor of the Sponsors.
	On July 2, 2013, the Company completed an IPO of its common stock. Using a portion of the net proceeds from the IPO, the Company paid a $24.4 million termination fee to affiliates of the Sponsors in connection with the termination of the management services agreement with such entities that was effective upon completion of the IPO. The Company paid an annual management fee of $2.5 million and $5.0 million in the years ended December 31, 2013 and 2012, respectively. There was no management fee paid for the year ended December 31, 2014.
	On March 20, 2014, the Company repurchased and subsequently canceled $25.0 million aggregate principal amount of the 2019 Senior Notes from an affiliate of Providence Equity. See Note 7 for additional information related to this transaction.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment Information	Segment Information
	Segment information is presented in accordance with a “management approach,” which designates the internal reporting used by the chief operating decision-maker for making decisions and assessing performance as the source of the Company's reportable segments. The Company's segments are organized in a manner consistent with which separate financial information is available and evaluated regularly by the chief operating decision-maker in deciding how to allocate resources and in assessing performance.
	The Company has two reportable segments: Corporate, which is comprised primarily of business customers, and Public, which is comprised of government entities and education and healthcare institutions. The Company also has three other operating segments, CDW Advanced Services, Canada and Kelway, which do not meet the reportable segment quantitative thresholds and, accordingly, are combined together as “Other.” In November 2014, the Company acquired a 35% non-controlling equity interest in Kelway. See Note 15 for additional information on Kelway.
	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 both the Corporate 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 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. Depreciation expense is included in Headquarters as it is not allocated among segments or used in measuring segment performance.
	IPO- and secondary-offering related expenses primarily relating to coworker compensation were included within operating segment results for the year ended December 31, 2013. See Note 9 for additional discussion of IPO- and secondary-offering related expenses.
	The Company allocates resources to and evaluates performance of its segments based on net sales, income (loss) from operations and Adjusted EBITDA, a non-GAAP measure as defined in the Company's credit agreements. However, the Company has concluded that income (loss) 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
	The following table presents information about the Company’s segments for the years ended December 31, 2014, 2013 and 2012:
	(in millions)	Corporate			Public				Other				Headquarters				Total
	2014:00:00
	Net sales	$	6,475.50		$	4,879.40			$	719.6			$	—			$	12,074.50
	Income (loss) from operations	439.8			313.2				32.9				(112.9		)		673
	Depreciation and amortization expense	(96.3		)	(43.8		)		(8.8		)		(59.0		)		(207.9		)
	2013:00:00
	Net sales	$	5,960.10		$	4,164.50			$	644			$	—			$	10,768.60
	Income (loss) from operations(1)	363.3			246.5				27.2				(128.4		)		508.6
	Depreciation and amortization expense	(97.3		)	(44.0		)		(8.6		)		(58.3		)		(208.2		)
	2012:00:00
	Net sales	$	5,512.80		$	4,023.00			$	592.4			$	—			$	10,128.20
	Income (loss) from operations	349			246.7				18.6				(103.7		)		510.6
	Depreciation and amortization expense	(97.6		)	(44.0		)		(9.3		)		(59.3		)		(210.2		)
	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.
	Major Customers, Geographic Areas, and Product Mix
	Net sales to the federal government were $884.2 million, $764.4 million and $964.7 million and accounted for approximately 7%, 7% and 10% of total net sales in 2014, 2013 and 2012, respectively. Net sales to customers outside of the U.S., primarily in Canada, were approximately 4% of the Company's total net sales in 2014, 2013 and 2012. Approximately 1% of the Company’s long-lived assets were located outside of the U.S. as of December 31, 2014 and 2013.
	The following table presents net sales by major category for the years ended December 31, 2014, 2013 and 2012. Categories are based upon internal classifications. Amounts for the years ended December 31, 2013 and 2012 have been reclassified for certain changes in individual product classifications to conform to the presentation for the year ended December 31, 2014.
		Year Ended						Year Ended							Year Ended
		December 31, 2014						December 31, 2013							December 31, 2012
		Dollars in			Percentage			Dollars in				Percentage			Dollars in				Percentage
		Millions			of Total Net			Millions				of Total Net			Millions				of Total Net
					Sales							Sales							Sales
	Notebooks/Mobile Devices	$	2,352.30		19.5	%		$	1,698.40			15.8	%		$	1,462.80			14.4	%
	NetComm Products	1,615.90			13.4			1,486.30				13.8			1,351.50				13.3
	Enterprise and Data Storage (Including Drives)	1,024.30			8.5			999.2				9.3			981.5				9.7
	Other Hardware	4,549.20			37.6			4,178.50				38.8			4,075.70				40.3
	Software	2,076.70			17.2			1,993.10				18.5			1,877.70				18.5
	Services	371.4			3.1			332.7				3.1			285				2.8
	Other (1)	84.7			0.7			80.4				0.7			94				1
	Total net sales	$	12,074.50		100	%		$	10,768.60			100	%		$	10,128.20			100	%
	-1	Includes items such as delivery charges to customers and certain commission revenue.

Supplemental_Guarantor_Informa

Supplemental Guarantor Information	12 Months Ended
	Dec. 31, 2014
Supplemental Guarantor Information [Abstract]
Supplemental Guarantor Information	Supplemental Guarantor Information
	The 2019 Senior Notes, the 2022 Senior Notes, and the 2024 Senior Notes are, and, prior to being redeemed in full, the Senior Subordinated Notes and the Senior Secured Notes, were guaranteed by Parent and each of CDW LLC’s direct and indirect, 100% owned, domestic subsidiaries (the “Guarantor Subsidiaries”). All guarantees by Parent and 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 2019 Senior Notes, the 2022 Senior Notes, and the 2024 Senior Notes, and (ii) were subject to certain customary release provisions contained in the indentures governing the Senior Subordinated Notes and the Senior Secured Notes until such indentures were satisfied and discharged in 2014. CDW LLC's Canada subsidiary (the “Non-Guarantor Subsidiary”) does 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 Subsidiary is 100% owned by CDW LLC.
	On May 9, 2014, all of the remaining $42.5 million aggregate principal amount of Senior Subordinated Notes was redeemed in full and the indenture governing the Senior Subordinated Notes was satisfied and discharged. See Note 7 for more information.
	On August 5, 2014, CDW LLC and CDW Finance Corporation, as co-issuers, completed the issuance of $600.0 million aggregate principal amount of 2022 Senior Notes, which is guaranteed by Parent and the Guarantor Subsidiaries. The proceeds from this issuance, along with cash on hand, were used to redeem all of the remaining $325.0 million aggregate principal amount of the Senior Secured Notes and to redeem $234.7 million aggregate principal amount of the 2019 Senior Notes. The indenture governing the Senior Secured Notes was concurrently satisfied and discharged. See Note 7 for more information.
	On December 1, 2014, CDW LLC and CDW Finance Corporation, as co-issuers, completed the issuance of $575.0 million aggregate principal amount of 2024 Senior Notes, which is guaranteed by Parent and the Guarantor Subsidiaries. The proceeds from this issuance, along with cash on hand, were used to redeem $541.4 million aggregate principal amount of the 8.5% Senior Notes. See Note 7 for more information.
	The following tables set forth condensed consolidating balance sheets as of December 31, 2014 and 2013, consolidating statements of operations for the years ended December 31, 2014, 2013 and 2012, condensed consolidating statements of comprehensive income for the years ended December 31, 2014, 2013 and 2012, and condensed consolidating statements of cash flows for the years ended December 31, 2014, 2013 and 2012, 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 accounts of the Non-Guarantor Subsidiary, 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, 2014
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Assets
	Current assets:
	Cash and cash equivalents	$	—		$	346.4		$	—		$	24.6		$	—	$	(26.5	)	$	344.5
	Accounts receivable, net	—			—			1,479.10			82			—		—			1,561.10
	Merchandise inventory	—			—			333.9			3.6			—		—			337.5
	Miscellaneous receivables	—			56.1			93.3			6.2			—		—			155.6
	Prepaid expenses and other	—			11			46			1.5			—		(3.8		)	54.7
	Total current assets	—			413.5			1,952.30			117.9			—		(30.3		)	2,453.40
	Property and equipment, net	—			80.5			55.5			1.2			—		—			137.2
	Equity investments	—			86.7			—			—			—		—			86.7
	Goodwill	—			751.8			1,439.00			26.8			—		—			2,217.60
	Other intangible assets, net	—			320			843.6			5.2			—		—			1,168.80
	Deferred financing costs, net	—			33			—			—			—		—			33
	Other assets	4.3			3.2			0.4			1.4			—		(6.1		)	3.2
	Investment in and advances to subsidiaries	932.2			2,784.50			—			—			—		(3,716.7		)	—
	Total assets	$	936.5		$	4,473.20		$	4,290.80		$	152.5		$	—	$	(3,753.1	)	$	6,099.90
	Liabilities and Shareholders’ Equity
	Current liabilities:
	Accounts payable-trade	$	—		$	23.9		$	671.9		$	34.7		$	—	$	(26.5	)	$	704
	Accounts payable-inventory financing	—			—			332.1			—			—		—			332.1
	Current maturities of long-term debt	—			15.4			—			—			—		—			15.4
	Deferred revenue	—			—			79.9			1.4			—		—			81.3
	Accrued expenses	—			137.8			193.6			7.9			—		(4.1		)	335.2
	Total current liabilities	—			177.1			1,277.50			44			—		(30.6		)	1,468.00
	Long-term liabilities:
	Debt	—			3,174.60			—			—			—		—			3,174.60
	Deferred income taxes	—			146.7			331.3			1.3			—		(4.3		)	475
	Other liabilities	—			42.6			3.7			1			—		(1.5		)	45.8
	Total long-term liabilities	—			3,363.90			335			2.3			—		(5.8		)	3,695.40
	Total shareholders’ equity	936.5			932.2			2,678.30			106.2			—		(3,716.7		)	936.5
	Total liabilities and shareholders' equity	$	936.5		$	4,473.20		$	4,290.80		$	152.5		$	—	$	(3,753.1	)	$	6,099.90
	Condensed Consolidating Balance Sheet
	December 31, 2013
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Assets
	Current assets:
	Cash and cash equivalents	$	—		$	196.5		$	—		$	14		$	—	$	(22.4	)	$	188.1
	Accounts receivable, net	—			—			1,375.90			75.1			—		—			1,451.00
	Merchandise inventory	—			—			378.9			3.1			—		—			382
	Miscellaneous receivables	—			49.9			91			5.4			—		—			146.3
	Prepaid expenses and other	—			10.7			33.4			5.1			—		(3.1		)	46.1
	Total current assets	—			257.1			1,879.20			102.7			—		(25.5		)	2,213.50
	Property and equipment, net	—			69.7			59.6			1.8			—		—			131.1
	Goodwill	—			751.9			1,439.00			29.4			—		—			2,220.30
	Other intangible assets, net	—			338.5			982.8			6.7			—		—			1,328.00
	Deferred financing costs, net	—			30.1			—			—			—		—			30.1
	Other assets	4.9			1.4			0.1			0.9			—		(5.7		)	1.6
	Investment in and advances to subsidiaries	706.8			2,909.40			—			—			—		(3,616.2		)	—
	Total assets	$	711.7		$	4,358.10		$	4,360.70		$	141.5		$	—	$	(3,647.4	)	$	5,924.60
	Liabilities and Shareholders' Equity
	Current liabilities:
	Accounts payable-trade	$	—		$	21.4		$	637.3		$	26.5		$	—	$	(22.4	)	$	662.8
	Accounts payable-inventory financing	—			—			256.6			—			—		—			256.6
Current maturities of long-term debt	—			45.4			—			—			—		—			45.4
Deferred revenue	—			—			89.9			4.9			—		—			94.8
Accrued expenses	—			163.5			175.1			7.5			—		(3.1		)	343
Total current liabilities	—			230.3			1,158.90			38.9			—		(25.5		)	1,402.60
Long-term liabilities:
Debt	—			3,205.80			—			—			—		—			3,205.80
Deferred income taxes	—			178.3			388.4			1.6			—		(4.8		)	563.5
Other liabilities	—			36.9			3.6			1.4			—		(0.9		)	41
Total long-term liabilities	—			3,421.00			392			3			—		(5.7		)	3,810.30
Total shareholders’ equity	711.7			706.8			2,809.80			99.6			—		(3,616.2		)	711.7
Total liabilities and shareholders’ equity	$	711.7		$	4,358.10		$	4,360.70		$	141.5		$	—	$	(3,647.4	)	$	5,924.60
Consolidating Statement of Operations
Year Ended December 31, 2014
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Net sales	$	—		$	—		$	11,542.30		$	532.2		$	—	$	—		$	12,074.50
Cost of sales	—			—			9,684.90			468.3			—		—			10,153.20
Gross profit	—			—			1,857.40			63.9			—		—			1,921.30
Selling and administrative expenses	—			112.8			962.3			35.2			—		—			1,110.30
Advertising expense	—			—			134			4			—		—			138
(Loss) income from operations	—			(112.8		)	761.1			24.7			—		—			673
Interest (expense) income, net	—			(197.7		)	0.1			0.3			—		—			(197.3		)
Net loss on extinguishments of long-term debt	—			(90.7		)	—			—			—		—			(90.7		)
Management fee	—			3.9			—			(3.9		)	—		—			—
Other income, net	—			1.2			1.5			—			—		—			2.7
(Loss) income before income taxes	—			(396.1		)	762.7			21.1			—		—			387.7
Income tax benefit (expense)	—			141			(278.1		)	(5.7		)	—		—			(142.8		)
(Loss) income before equity in earnings of subsidiaries	—			(255.1		)	484.6			15.4			—		—			244.9
Equity in earnings of subsidiaries	244.9			500			—			—			—		(744.9		)	—
Net income	$	244.9		$	244.9		$	484.6		$	15.4		$	—	$	(744.9	)	$	244.9
Consolidating Statement of Operations
Year Ended December 31, 2013
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Net sales	$	—		$	—		$	10,293.30		$	475.3		$	—	$	—		$	10,768.60
Cost of sales	—			—			8,592.10			416.2			—		—			9,008.30
Gross profit	—			—			1,701.20			59.1			—		—			1,760.30
Selling and administrative expenses	24.4			103.9			957.3			35.3			—		—			1,120.90
Advertising expense	—			—			126.8			4			—		—			130.8
(Loss) income from operations	(24.4		)	(103.9		)	617.1			19.8			—		—			508.6
Interest (expense) income, net	—			(250.6		)	0.2			0.3			—		—			(250.1		)
Net loss on extinguishments of long-term debt	—			(64.0		)	—			—			—		—			(64.0		)
Management fee	—			4.3			—			(4.3		)	—		—			—
Other (expense) income, net	—			(0.5		)	1.2			0.3			—		—			1
(Loss) income before income taxes	(24.4		)	(414.7		)	618.5			16.1			—		—			195.5
Income tax benefit (expense)	9.2			142.2			(209.5		)	(4.6		)	—		—			(62.7		)
(Loss) income before equity in earnings of subsidiaries	(15.2		)	(272.5		)	409			11.5			—		—			132.8
Equity in earnings of subsidiaries	148			420.5			—			—			—		(568.5		)	—
Net income	$	132.8		$	148		$	409		$	11.5		$	—	$	(568.5	)	$	132.8
Consolidating Statement of Operations
Year Ended December 31, 2012
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Net sales	$	—		$	—		$	9,683.00		$	445.2		$	—	$	—		$	10,128.20
Cost of sales	—			—			8,071.50			387.1			—		—			8,458.60
Gross profit	—			—			1,611.50			58.1			—		—			1,669.60
Selling and administrative expenses	—			103.7			891.6			34.2			—		—			1,029.50
Advertising expense	—			—			125.1			4.4			—		—			129.5
(Loss) income from operations	—			(103.7		)	594.8			19.5			—		—			510.6
Interest (expense) income, net	—			(308.0		)	0.4			0.2			—		—			(307.4		)
Net loss on extinguishments of long-term debt	—			(17.2		)	—			—			—		—			(17.2		)
Management fee	—			3.8			—			(3.8		)	—		—			—
Other income (expense), net	—			—			0.2			(0.1		)	—		—			0.1
(Loss) income before income taxes	—			(425.1		)	595.4			15.8			—		—			186.1
Income tax benefit (expense)	—			210.6			(272.6		)	(5.1		)	—		—			(67.1		)
(Loss) income before equity in earnings of subsidiaries	—			(214.5		)	322.8			10.7			—		—			119
Equity in earnings of subsidiaries	119			333.5			—			—			—		(452.5		)	—
Net income	$	119		$	119		$	322.8		$	10.7		$	—	$	(452.5	)	$	119
Condensed Consolidating Statement of Comprehensive Income
Year Ended December 31, 2014
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Comprehensive income	$	234.6		$	234.6		$	484.6		$	5.1		$	—	$	(724.3	)	$	234.6
Condensed Consolidating Statement of Comprehensive Income
Year Ended December 31, 2013
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Comprehensive income	$	126.1		$	141.3		$	409		$	4.8		$	—	$	(555.1	)	$	126.1
Condensed Consolidating Statement of Comprehensive Income
Year Ended December 31, 2012
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Comprehensive income	$	121.5		$	121.5		$	322.8		$	13.2		$	—	$	(457.5	)	$	121.5
Condensed Consolidating Statement of Cash Flows
Year Ended December 31, 2014
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Net cash (used in) provided by operating activities	$	—		$	(120.4	)	$	547.7		$	11.8		$	—	$	(4.1	)	$	435
Cash flows from investing activities:
Capital expenditures	—			(47.9		)	(7.1		)	—			—		—			(55.0		)
Payment for equity investments	—			(86.8		)	—			—			—		—			(86.8		)
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	—			(20.9		)	—			—			—		—			(20.9		)
Premium payments on interest rate cap agreements	—			(2.1		)	—			—			—		—			(2.1		)
Net cash used in investing activities	—			(157.7		)	(7.1		)	—			—		—			(164.8		)
Cash flows from financing activities:
Repayments of long-term debt	—			(15.4		)	—			—			—		—			(15.4		)
Proceeds from issuance of long-term debt	—			1,175.00			—			—			—		—			1,175.00
Payments to extinguish long-term debt	—			(1,299.0		)	—			—			—		—			(1,299.0		)
Payment of debt financing costs	—			(21.9		)	—			—			—		—			(21.9		)
Net change in accounts payable-inventory financing	—			—			75.5			—			—		—			75.5
Proceeds from stock option exercises	—			1.3			—			—			—		—			1.3
Proceeds from Coworker stock purchase plan	—			5.8			—			—			—		—			5.8
Dividends paid	(33.6		)	—			—			—			—		—			(33.6		)
Excess tax benefits from equity-based compensation	—			0.3			—			—			—		—			0.3
Advances to/from affiliates	33.6			581.9			(616.1		)	0.6			—		—			—
Net cash provided by (used in) financing activities	—			428			(540.6		)	0.6			—		—			(112.0		)
Effect of exchange rate changes on cash and cash equivalents	—			—			—			(1.8		)	—		—			(1.8		)
Net increase in cash and cash equivalents	—			149.9			—			10.6			—		(4.1		)	156.4
Cash and cash equivalents – beginning of period	—			196.5			—			14			—		(22.4		)	188.1
Cash and cash equivalents – end of period	$	—		$	346.4		$	—		$	24.6		$	—	$	(26.5	)	$	344.5
Condensed Consolidating Statement of Cash Flows
Year Ended December 31, 2013
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Net cash (used in) provided by operating activities	$	(15.2	)	$	(130.3	)	$	508.8		$	5.5		$	—	$	(2.5	)	$	366.3
Cash flows from investing activities:
Capital expenditures	—			(40.8		)	(6.2		)	(0.1		)	—		—			(47.1		)
Net cash used in investing activities	—			(40.8		)	(6.2		)	(0.1		)	—		—			(47.1		)
Cash flows from financing activities:
Proceeds from borrowings under revolving credit facility	—			63			—			—			—		—			63
Repayments of borrowings under revolving credit facility	—			(63.0		)	—			—			—		—			(63.0		)
Repayments of long-term debt	—			(51.1		)	—			—			—		—			(51.1		)
Proceeds from issuance of long-term debt	—			1,535.20			—			—			—		—			1,535.20
Payments to extinguish long-term debt	—			(2,047.4		)	—			—			—		—			(2,047.4		)
Payment of debt financing costs	—			(6.1		)	—			—			—		—			(6.1		)
Net change in accounts payable-inventory financing	—			—			7.4			—			—		—			7.4
Payment of incentive compensation plan withholding taxes	—			(4.0		)	(19.6		)	(0.5		)	—		—			(24.1		)
Net proceeds from issuance of common shares	424.7			—			—			—			—		—			424.7
Dividends paid	(7.3		)	—			—			—			—		—			(7.3		)
Advances to/from affiliates	(402.2		)	892.6			(490.4		)	—			—		—			—
Other financing activities	—			0.4			—			—			—		—			0.4
Net cash provided by (used in) financing activities	15.2			319.6			(502.6		)	(0.5		)	—		—			(168.3		)
Effect of exchange rate changes on cash and cash equivalents	—			—			—			(0.7		)	—		—			(0.7		)
Net increase in cash and cash equivalents	—			148.5			—			4.2			—		(2.5		)	150.2
Cash and cash equivalents – beginning of period	—			48			—			9.8			—		(19.9		)	37.9
Cash and cash equivalents – end of period	$	—		$	196.5		$	—		$	14		$	—	$	(22.4	)	$	188.1
Condensed Consolidating Statement of Cash Flows
Year Ended December 31, 2012
(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
	Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
Net cash (used in) provided by operating activities	$	—		$	(204.3	)	$	514.2		$	1.3		$	—	$	6.2		$	317.4
Cash flows from investing activities:
Capital expenditures	—			(27.0		)	(14.0		)	(0.4		)	—		—			(41.4		)
Premium payments on interest rate cap agreements	—			(0.3		)	—			—			—		—			(0.3		)
Net cash used in investing activities	—			(27.3		)	(14.0		)	(0.4		)	—		—			(41.7		)
Cash flows from financing activities:
Proceeds from borrowings under revolving credit facility	—			289			—			—			—		—			289
Repayments of borrowings under revolving credit facility	—			(289.0		)	—			—			—		—			(289.0		)
Repayments of long-term debt	—			(201.0		)	—			—			—		—			(201.0		)
Proceeds from issuance of long-term debt	—			135.7			—			—			—		—			135.7
Payments to extinguish long-term debt	—			(243.2		)	—			—			—		—			(243.2		)
Payment of debt financing costs	—			(2.1		)	—			—			—		—			(2.1		)
Net change in accounts payable-inventory financing	—			—			(29.5		)	—			—		—			(29.5		)
Advances to/from affiliates	—			486			(486.5		)	0.5			—		—			—
Other financing activities	—			2.1			—			—			—		—			2.1
Net cash provided by (used in) financing activities	—			177.5			(516.0		)	0.5			—		—			(338.0		)
Effect of exchange rate changes on cash and cash equivalents	—			—			—			0.3			—		—			0.3
Net (decrease) increase in cash and cash equivalents	—			(54.1		)	(15.8		)	1.7			—		6.2			(62.0		)
Cash and cash equivalents – beginning of period	—			102.1			15.8			8.1			—		(26.1		)	99.9
Cash and cash equivalents – end of period	$	—		$	48		$	—		$	9.8		$	—	$	(19.9	)	$	37.9

Selected_Quarterly_Financial_R

Selected Quarterly Financial Results	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Selected Quarterly Financial Results	Selected Quarterly Financial Results (unaudited)
	(in millions, except per-share amounts)	2014
		First Quarter		Second Quarter		Third Quarter			Fourth Quarter
	Net Sales Detail:
	Corporate:
	Medium/Large	$	1,274.80	$	1,395.40	$	1,374.80		$	1,440.30
	Small Business	230.8		260.8		247.9			250.7
	Total Corporate	1,505.60		1,656.20		1,622.70			1,691.00
	Public:
	Government	254.2		313.1		441.3			440.8
	Education	321.6		527		632.8			342.6
	Healthcare	394.1		431.5		394.7			385.7
	Total Public	969.9		1,271.60		1,468.80			1,169.10
	Other	176.8		178.2		174.6			190
	Net sales	$	2,652.30	$	3,106.00	$	3,266.10		$	3,050.10
	Gross profit	$	425.2	$	496.9	$	507.3		$	491.9
	Income from operations	135.8		188.2		184.7			164.3
	Net income	50.9		86.6		55.6			51.8
	Net income per common share  (1):
	Basic	0.3		0.51		0.33			$	0.3
	Diluted	0.3		0.5		0.32			$	0.3
	(in millions, except per-share amounts)	2013
		First Quarter		Second Quarter		Third Quarter			Fourth Quarter
	Net Sales Detail:
	Corporate:
	Medium/Large (2)	$	1,180.50	$	1,308.50	$	1,241.30		$	1,322.30
	Small Business (2)	223.4		228.9		224.5			230.7
	Total Corporate	1,403.90		1,537.40		1,465.80			1,553.00
	Public:
	Government	252.3		295.7		375.3			327.3
	Education	232.2		420.6		513.4			282.8
	Healthcare	362.3		366.3		355.9			380.4
	Total Public	846.8		1,082.60		1,244.60			990.5
	Other	161		159.3		153.9			169.8
	Net sales	$	2,411.70	$	2,779.30	$	2,864.30		$	2,713.30
	Gross profit	$	402	$	451.6	$	458.4		$	448.3
	Income from operations (3)	120.1		153.6		92.9			142
	Net income (loss)(3)	28.3		46.7		(2.2		)	60
	Net income (loss) per common share (1)(3):
	Basic	0.19		0.32		(0.01		)	0.35
	Diluted	0.19		0.32		(0.01		)	0.35
	-1	Basic and diluted net income (loss) 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 (loss) per share.
	-2	Net sales for the corporate channels (medium/large and small business) have been restated for all periods presented above to conform with the new corporate hierarchy presented for first quarter of 2014.
	-3	The third quarter of 2013 included pre-tax IPO-related charges of $74.1 million. See Note 9 for additional discussion of the IPO.

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Event [Line Items]
Subsequent Events [Text Block]	Subsequent Events
	During the first quarter of 2015, the Company entered into six interest rate cap agreements with a combined notional amount of $400.0 million. Under the agreements, the Company made premium payments totaling $0.5 million to the counterparties in exchange for the right to receive payments equal to the amount, if any, by which three-month LIBOR exceeds 2.0% during the agreement period. The interest rate cap agreements are effective from January 14, 2015 through January 14, 2017.
	On February 10, 2015, the Company announced that its board of directors declared a cash dividend on the Company's common stock of $0.0675 per share. The dividend will be paid on March 10, 2015 to all stockholders of record as of the close of business on February 25, 2015. Future dividends will be subject to the approval of the Company's board of directors.

Valuation_And_Qualifying_Accou

Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Valuation And Qualifying Accounts	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS
	Years ended December 31, 2014, 2013 and 2012
	(in millions)	Balance at		Charged to		Deductions			Balance at
		Beginning		Costs and					End of
		of Period		Expenses					Period
	Allowance for doubtful accounts:
	Year Ended December 31, 2014	$	5.4	$	5.4	$	(5.1	)	$	5.7
	Year Ended December 31, 2013	5.4		2.8		(2.8		)	5.4
	Year Ended December 31, 2012	5.4		3.9		(3.9		)	5.4
	Reserve for sales returns:
	Year Ended December 31, 2014	$	5.1	$	36.2	$	(36.2	)	$	5.1
	Year Ended December 31, 2013	4.4		35		(34.3		)	5.1
	Year Ended December 31, 2012	4.5		33.2		(33.3		)	4.4

Description_Of_Business_And_Su1

Description Of Business And Summary Of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Description of Business and Summary of Significant Accounting Policies [Abstract]
Description of Business [Policy Text Block]	Description of Business
	CDW Corporation ("Parent") is a Fortune 500 company and a leading provider of integrated information technology (“IT”) solutions to small, medium and large business, government, education and healthcare customers in the U.S. 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. On August 6, 2010, CDW Finance Corporation, a Delaware corporation, was formed for the sole purpose of acting as co-issuer of certain debt obligations as described in Note 18 and does not hold any material assets or engage in any business activities or operations.
	CDW Corporation was previously owned directly by CDW Holdings LLC ("CDW Holdings"), a company controlled by investment funds affiliated with Madison Dearborn Partners, LLC ("Madison Dearborn") and Providence Equity Partners L.L.C. ("Providence Equity," and together with Madison Dearborn, the "Sponsors"), certain other co-investors and certain members of CDW management. On July 2, 2013, Parent completed an initial public offering ("IPO") of its common stock. In connection with the IPO, CDW Holdings distributed all of its shares of Parent's common stock to its members in June 2013 in accordance with the members’ respective membership interests and was subsequently dissolved in August 2013. See Note 9 for additional discussion of the IPO.
Basis of Accounting, Policy	Basis of Presentation
	The accompanying 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 U.S. Securities and Exchange Commission (“SEC”).
Consolidation, Policy	Principles of Consolidation
	The accompanying 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, Policy	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 at 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.
Cash and Cash Equivalents, Policy	Cash and Cash Equivalents
	Cash and cash equivalents include all deposits in banks and short-term (original maturities of three months or less), 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, Policy	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.
Merchandise Inventory, Policy	Merchandise Inventory
	Inventory is valued at the lower of cost or market 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 estimated market 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, Policy	Miscellaneous Receivables
	Miscellaneous receivables generally consist of amounts due from vendors. The Company receives incentives from vendors related to cooperative advertising allowances, 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 inventory, depending on the nature of the incentive.
Property, Plant and Equipment, Policy	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. Leasehold improvements are amortized over the shorter of their 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 following table shows estimated useful lives of property and equipment:
	Classification	Estimated
		Useful Lives
	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 operating leases to its original condition upon lease termination. The Company’s asset retirement liability was $0.5 million as of December 31, 2014 and 2013.
Equity Method Investments, Policy [Policy Text Block]	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 net income or loss of equity method investees is included in other income, net in the consolidated statements of operations.
Goodwill and Other Intangible Assets, Policy	Goodwill and Other Intangible Assets
	The Company is required to perform an evaluation of goodwill on an annual basis 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 used to assess potential goodwill impairment are the same as its operating segments. The Company has the option of performing a qualitative assessment of a reporting unit's fair value from the last quantitative assessment to determine if it is more likely than not that the reporting unit's goodwill is impaired or performing a quantitative assessment by comparing a reporting unit's estimated fair value to its carrying amount. Under the quantitative assessment, testing for impairment of goodwill is a two-step process. The first step compares the fair value of a reporting unit with its carrying amount, including goodwill. If the carrying amount of a reporting unit exceeds its fair value, the second step compares the implied fair value of reporting unit goodwill with the carrying amount of that goodwill to determine the amount of impairment loss. Fair value of a reporting unit is determined by using a weighted combination of an income approach and a market approach, as this combination is considered the most indicative of the Company’s fair value in an orderly transaction between market participants. This assessment uses significant accounting judgments, estimates and assumptions. Any changes in the judgments, estimates or assumptions used could produce significantly different results. During the years ended December 31, 2014, 2013 and 2012, the Company concluded its goodwill was not impaired. See Note 4 for more information on the Company’s evaluations of goodwill for impairment.
	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. These intangible assets are reviewed for impairment when indicators are present using undiscounted cash flows. The Company uses the undiscounted cash flows, excluding interest charges, to assess the recoverability of the carrying value of such assets. To the extent carrying value exceeds the undiscounted cash flows, an impairment loss is recorded based upon the excess of the carrying value over 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. During the years ended December 31, 2014, 2013 and 2012, no impairment existed with respect to the Company’s intangible assets with determinable lives and no significant changes to the remaining useful lives were necessary. The following table shows estimated useful lives of definite-lived intangible assets:
	Classification	Estimated
		Useful Lives
	Customer relationships	11 to 14 years
	Trade name	20 years
	Internally developed software	3 to 5 years
	Other	1 to 10 years
Deferred Charges, Policy	Deferred Financing Costs
	Deferred financing costs, such as underwriting, financial advisory, professional fees and other similar fees are capitalized and recognized in interest expense over the estimated life of the related debt instrument using the effective interest method or straight-line method, as applicable.
Derivatives, Policy	Derivatives
	The Company has entered into interest rate cap agreements for the purpose of economically hedging its exposure to fluctuations in interest rates. These derivatives are recorded at fair value in the Company’s consolidated balance sheets.
	The Company’s interest rate cap agreements are not designated as cash flow hedges of interest rate risk. Changes in fair value of the derivatives are recorded directly to interest expense in the Company’s consolidated statements of operations.
Fair Value Measurement, Policy	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 Income, Policy	Accumulated Other Comprehensive (Loss) Income
	Foreign currency translation adjustments are included in shareholders’ equity under accumulated other comprehensive (loss) income.
	The components of accumulated other comprehensive (loss) income are as follows:
	(in millions)	December 31,
		2014			2013			2012
	Foreign currency translation adjustment	$	(16.6	)	$	(6.3	)	$	0.4
	Accumulated other comprehensive (loss) income	$	(16.6	)	$	(6.3	)	$	0.4
Revenue Recognition, Policy	Revenue Recognition
	The Company is a primary distribution channel for a large group of vendors and suppliers, including original equipment manufacturers (“OEMs”), software publishers and wholesale distributors. 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 products and 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 or recognized using a proportional performance model for services provided at a fixed fee. Revenue from cloud computing solutions including Software as a Service ("SaaS") and Infrastructure as a Service ("IaaS") arrangements, as well as data center services such as managed and remote managed services, server co-location, internet connectivity and data backup and storage, is 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.
	From time to time, the Company 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. 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 (1) payments received from customers in advance of providing the product or performing services, and (2) 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 Tax, Policy	Sales Taxes
	Sales tax amounts collected from customers for remittance to governmental authorities are presented on a net basis in the Company’s consolidated statements of operations.
Advertising Cost, Policy	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, Policy	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, Policy	Interest Expense
	Interest expense is typically recognized in the period incurred at the applicable interest rate in effect. For increasing-rate debt, the Company determines the periodic interest cost using the effective interest method over the estimated outstanding term of the debt. The difference between interest expense recorded and cash interest paid is reflected as short-term or long-term accrued interest in the Company’s consolidated balance sheets.
Foreign Currency Translation, Policy	Foreign Currency Translation
	The Company’s functional currency is the U.S. dollar. The functional currency of the Company’s Canadian subsidiary is the local currency, the Canadian dollar. The functional currency of the Company's equity investment in Kelway TopCo Limited ("Kelway") is the local currency, the British pound sterling.  Assets and liabilities of the Canadian subsidiary and the Company’s share of assets and liabilities in Kelway are translated at the spot rate in effect at the applicable reporting date and the consolidated results of operations of the Canadian subsidiary and the Company’s share of the net income or loss of Kelway 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) income, which is reflected as a separate component of shareholders’ equity.
Income Tax, Policy	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.

Description_Of_Business_And_Su2

Description Of Business And Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accumulated Other Comprehensive Loss [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The components of accumulated other comprehensive (loss) income are as follows:
	(in millions)	December 31,
		2014			2013			2012
	Foreign currency translation adjustment	$	(16.6	)	$	(6.3	)	$	0.4
	Accumulated other comprehensive (loss) income	$	(16.6	)	$	(6.3	)	$	0.4
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets [Table Text Block]	The following table shows estimated useful lives of definite-lived intangible assets:
	Classification	Estimated
		Useful Lives
	Customer relationships	11 to 14 years
	Trade name	20 years
	Internally developed software	3 to 5 years
	Other	1 to 10 years
	The following table presents a summary of intangible assets at December 31, 2014 and 2013:
	(in millions)
	December 31, 2014		Gross			Accumulated			Net Carrying Amount
			Carrying			Amortization
			Amount
	Customer relationships		$	1,859.70		$	1,012.10		$	847.6
	Trade name		421			152			269
	Internally developed software		110.1			58.9			51.2
	Other		3.2			2.2			1
	Total		$	2,394.00		$	1,225.20		$	1,168.80
	December 31, 2013
	Customer relationships		$	1,860.80		$	872.8		$	988
	Trade name		421			130.9			290.1
	Internally developed software		128.5			79.8			48.7
	Other		3.1			1.9			1.2
	Total		$	2,413.40		$	1,085.40		$	1,328.00
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Table Text Block]	The following table shows estimated useful lives of property and equipment:
	Classification	Estimated
		Useful Lives
	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 consisted of the following:
	(in millions)	December 31,
		2014			2013
	Land	$	27.7		$	27.7
	Machinery and equipment	54.3			53
	Building and leasehold improvements	105.1			104.8
	Computer and data processing equipment	65.6			61.2
	Computer software	10.6			30.9
	Furniture and fixtures	21.7			21.6
	Construction in progress	24.7			10.9
	Property and equipment	309.7			310.1
	Less: accumulated depreciation	172.5			179
	Property and equipment, net	$	137.2		$	131.1

Property_And_Equipment_Tables

Property And Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Table Text Block]	The following table shows estimated useful lives of property and equipment:
	Classification	Estimated
		Useful Lives
	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 consisted of the following:
	(in millions)	December 31,
		2014		2013
	Land	$	27.7	$	27.7
	Machinery and equipment	54.3		53
	Building and leasehold improvements	105.1		104.8
	Computer and data processing equipment	65.6		61.2
	Computer software	10.6		30.9
	Furniture and fixtures	21.7		21.6
	Construction in progress	24.7		10.9
	Property and equipment	309.7		310.1
	Less: accumulated depreciation	172.5		179
	Property and equipment, net	$	137.2	$	131.1

Goodwill_And_Other_Intangible_1

Goodwill And Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill [Table Text Block]	The following table presents the change in goodwill by segment for the years ended December 31, 2014 and 2013:
	(in millions)	Corporate			Public			Other (1)			Consolidated
	Balances as of December 31, 2012:
	Goodwill	$	2,794.40		$	1,261.40		$	107.3		$	4,163.10
	Accumulated impairment charges	(1,571.4		)	(354.1		)	(28.3		)	(1,953.8		)
		$	1,223.00		$	907.3		$	79		$	2,209.30
	2013 Activity:
	Translation adjustment	$	—		$	—		$	(2.1	)	$	(2.1	)
	Contingent consideration (2)	8.8			4			0.3			13.1
		$	8.8		$	4		$	(1.8	)	$	11
	Balances as of December 31, 2013:
	Goodwill	$	2,803.20		$	1,265.40		$	105.5		$	4,174.10
	Accumulated impairment charges	(1,571.4		)	(354.1		)	(28.3		)	(1,953.8		)
		$	1,231.80		$	911.3		$	77.2		$	2,220.30
	2014 Activity:
	Translation adjustment	$	—		$	—		$	(2.7	)	$	(2.7	)
		$	—		$	—		$	(2.7	)	$	(2.7	)
	Balances as of December 31, 2014:
	Goodwill	$	2,803.20		$	1,265.40		$	102.8		$	4,171.40
	Accumulated impairment charges	(1,571.4		)	(354.1		)	(28.3		)	(1,953.8		)
		$	1,231.80		$	911.3		$	74.5		$	2,217.60
	-1	Other is comprised of CDW Advanced Services, Canada, and Kelway reporting units. There is no goodwill attributable to the Kelway reporting unit.
	-2	During 2013, the Company recorded a $13.1 million net-of-tax addition to goodwill in connection with the settlement of the MPK Coworker Incentive Plan II and related charitable contribution. The charitable contribution was accounted for as additional purchase price (goodwill) in accordance with pre-2009 business combinations accounting guidance. See Note 10 for additional discussion of this transaction.
Schedule of Finite-Lived Intangible Assets [Table Text Block]	The following table shows estimated useful lives of definite-lived intangible assets:
	Classification	Estimated
		Useful Lives
	Customer relationships	11 to 14 years
	Trade name	20 years
	Internally developed software	3 to 5 years
	Other	1 to 10 years
	The following table presents a summary of intangible assets at December 31, 2014 and 2013:
	(in millions)
	December 31, 2014		Gross			Accumulated			Net Carrying Amount
			Carrying			Amortization
			Amount
	Customer relationships		$	1,859.70		$	1,012.10		$	847.6
	Trade name		421			152			269
	Internally developed software		110.1			58.9			51.2
	Other		3.2			2.2			1
	Total		$	2,394.00		$	1,225.20		$	1,168.80
	December 31, 2013
	Customer relationships		$	1,860.80		$	872.8		$	988
	Trade name		421			130.9			290.1
	Internally developed software		128.5			79.8			48.7
	Other		3.1			1.9			1.2
	Total		$	2,413.40		$	1,085.40		$	1,328.00
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	Estimated future amortization expense related to intangible assets for the next five years is as follows:
	(in millions)
	Years ending December 31,
	2015	$	180.7
	2016	172.8
	2017	167.1
	2018	160.4
	2019	158.9

Inventory_Financing_Agreements1

Inventory Financing Agreements (Tables)	12 Months Ended
	Dec. 31, 2014
Inventory Financing Agreements [Abstract]
Inventory Financing Agreements [Table Text Block]	The following table presents the amounts included in accounts payable-inventory financing:
	(in millions)	December 31,
		2014		2013
	Revolving Loan inventory financing agreement	$	330.1	$	256.1
	Other inventory financing agreements	2		0.5
	Accounts payable-inventory financing	$	332.1	$	256.6

Lease_Commitments_Tables

Lease Commitments (Tables)	12 Months Ended
	Dec. 31, 2014
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases of Lessee Disclosure [Table Text Block]	Future minimum lease payments are as follows:
	(in millions)
	Years ending December 31,
	2015	$	19.1
	2016	15.3
	2017	16.1
	2018	13.6
	2019	12.8
	Thereafter	50.6
	Total future minimum lease payments (1)	$	127.5
	(1) Included in these amounts are future minimum lease payments commencing in the fourth quarter of 2016 that relate to a new lease entered into in December 2014 for the Company’s future headquarters in Lincolnshire, Illinois. Also reflected in these amounts is the future expiration of two leases in the first quarter of 2016 for facilities currently in use by the Company which the Company plans to consolidate into the new headquarters location and accordingly, these leases will not be renewed

LongTerm_Debt_Tables

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Long-term Debt, Unclassified [Abstract]
Carrying Value of Long-Term Debt	Long-term debt was as follows:
	(dollars in millions)				December 31,
		Interest Rate (1)			2014				2013
	Senior secured asset-based revolving credit facility	—	%		$	—			$	—
	Senior secured term loan facility	3.25	%		1,513.50				1,528.90
	Unamortized discount on senior secured term loan facility				(3.7		)		(4.4		)
	Senior secured notes due 2018	—	%		—				325
	Senior notes due 2019	8.5	%		503.9				1,305.00
	Unamortized premium on senior notes due 2019				1.3				4.2
	Senior notes due 2022	6	%		600				—
	Senior notes due 2024	5.5	%		575				—
	Senior subordinated notes due 2017	—	%		—				92.5
	Total long-term debt				3,190.00				3,251.20
	Less current maturities of long-term debt				(15.4		)		(45.4		)
	Long-term debt, excluding current maturities				$	3,174.60			$	3,205.80
	(1)Interest rate at December 31, 2014.
Schedule of Long-term Debt Maturities	As of December 31, 2014, the maturities of long-term debt were as follows:
	(in millions)
	Years ending December 31,
	2015	$	15.4
	2016	—
	2017	—
	2018	—
	2019	503.9
	Thereafter	2,673.10
		$	3,192.40
Deferred Financing Costs Disclosure	The following table summarizes the deferred financing costs activity for the years ended December 31, 2014 and 2013:
	(in millions)	December 31,
		2014				2013
	Beginning balance	$	30.1			$	53.2
	Additional costs capitalized	21.9				6.1
	Recognized in interest expense	(6.4		)		(9.1		)
	Write-off of unamortized deferred financing costs	(12.6		)		(20.1		)
	Ending balance	$	33			$	30.1

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	Income before income taxes was taxed under the following jurisdictions:
	(in millions)	Years Ended December 31,
		2014			2013				2012
	Domestic	$	366.6		$	179.4			$	170.3
	Foreign	21.1			16.1				15.8
	Total	$	387.7		$	195.5			$	186.1
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Components of income tax expense (benefit) consisted of the following:
	(in millions)	Years Ended December 31,
		2014			2013				2012
	Current:
	Federal	$	206.8		$	96.7			$	110.3
	State	19.3			10.1				8
	Foreign	5.8			4.6				5.1
	Total current	231.9			111.4				123.4
	Deferred:
	Domestic	(89.0		)	(48.6		)		(56.2		)
	Foreign	(0.1		)	(0.1		)		(0.1		)
	Total deferred	(89.1		)	(48.7		)		(56.3		)
	Income tax expense	$	142.8		$	62.7			$	67.1
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The reconciliation between the statutory tax rate expressed as a percentage of income before income taxes and the effective tax rate is as follows:
	(dollars in millions)	Years Ended December 31,
		2014						2013						2012
	Statutory federal income tax rate	$	135.7		35	%		$	68.4			35	%	$	65.1		35	%
	State taxes, net of federal effect	6.5			1.6			(5.0		)		(2.6	)	0.4			0.2
	Equity-based compensation	1.1			0.3			1.5				0.7		5.7			3.1
	Effect of rates different than statutory	(1.9		)	(0.5	)		(1.4		)		(0.7	)	(1.4		)	(0.8	)
	Other	1.4			0.4			(0.8		)		(0.3	)	(2.7		)	(1.5	)
	Effective tax rate	$	142.8		36.8	%		$	62.7			32.1	%	$	67.1		36	%
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The tax effect of temporary differences that give rise to the net deferred income tax liability is presented below:
	(in millions)	December 31,
		2014			2013
	Deferred Tax Assets:
	Deferred interest	$	32.9		$	43.5
	State net operating loss and credit carryforwards, net	18.8			21.1
	Payroll and benefits	27			16.2
	Rent	5.5			6.4
	Accounts receivable	6.3			5.4
	Equity compensation plans	6.5			1.6
	Trade credits	1.5			1.5
	Other	5			7.1
	Total deferred tax assets	103.5			102.8
	Deferred Tax Liabilities:
	Software and intangibles	425.3			486.2
	Deferred income	116.2			145.5
	Property and equipment	22.5			25
	Other	15.3			11.6
	Total deferred tax liabilities	579.3			668.3
	Deferred tax asset valuation allowance	—			—
	Net deferred tax liability	$	475.8		$	565.5

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2014
IPO-related expenses [Abstract]
Shares sold by certain selling stockholders [Table Text Block]	The Company has completed the following secondary public offerings, whereby certain selling stockholders sold shares of common stock to the underwriters. The Company did not receive any proceeds from these sales of shares.
	Secondary Offering Shares			Completion Date of Secondary Offering	Overallotment Shares (1)		Completion Date of Overallotment Shares	Secondary Offering Expenses
								(in millions)
	15,000,000			11/19/13	2,250,000		12/18/13	$	0.6
	10,000,000			3/12/14	1,500,000		3/12/14	$	0.4
	15,000,000			5/28/14	2,250,000		6/4/14	$	0.5
	15,000,000			9/8/2014 (2)	—		—	$	0.3
	15,000,000			12/8/14	2,250,000		12/8/14	$	0.2
	(1) Under each underwriting agreement, the selling stockholders granted the underwriters an option, exercisable for thirty days, to purchase up to the additional amount of shares noted.
	(2) The option to purchase additional shares was not exercised in connection with the September 2014 secondary offering.
IPO- and secondary-offering related expenses [Table Text Block]	The following pre-tax IPO-related expenses and secondary-offering-related expenses were included within selling and administrative expenses in the consolidated statements of operations for the years ended December 31, 2014 and 2013, respectively.
	(in millions)	Year Ended December 31,
		2014			2013
	Acceleration charge for certain equity awards and related employer payroll taxes(1)	$	—		$	40.7
	RDU Plan cash retention pool accrual(2)	—			7.5
	Management services agreement termination fee(3)	—			24.4
	Other expenses (4)	1.4			2.4
	IPO- and secondary-offering-related expenses	$	1.4		$	75
	(1) See Note 10 for additional discussion of the impact of the IPO on the Company's equity awards.
	(2) See Note 12 for additional discussion of this transaction.
	(3) Represents the payment of a termination fee to affiliates of the Sponsors in connection with the termination of the management services agreement with such entities.
	(4) Other expenses include secondary-offering expenses of $1.4 million and $0.6 million for the years ended December 31, 2014 and 2013, respectively.

Shareholders_Equity_Dividends_

Shareholders' Equity Dividends Declared and paid (Tables)	12 Months Ended
	Dec. 31, 2014
Dividends Declared [Table Text Block]	The Company declared and paid cash dividends per common share during the periods presented as follows:
	(in millions, except per share amounts)	Dividends Per Share		Amount
	2014:00:00
	First Quarter	$	0.0425	$	7.3
	Second Quarter	0.0425		7.3
	Third Quarter	0.0425		7.3
	Fourth Quarter	0.0675		11.7
	2013:00:00
	First Quarter	$	—	$	—
	Second Quarter	—		—
	Third Quarter	—		—
	Fourth Quarter	0.0425		7.3

EquityBased_Compensation_Table

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Share-based Arrangements with Employees and Nonemployees [Abstract]
Schedule Equity-Based Compensation Expense [Table Text Block]	The following table summarizes equity-based compensation expense, which is included in selling and administrative expenses, for the years ended December 31, 2014, 2013 and 2012:
	(in millions)		Year Ended December 31,
			2014				2013 (1)			2012 (2)
	Equity-based compensation expense		$	16.4			$	46.6		$	22.1
	Income tax benefit		(5.1		)		(16.5		)	(2.3		)
	Total (net of tax)		$	11.3			$	30.1		$	19.8
	-1	Includes pre-tax expense of $36.7 million related to the accelerated vesting of certain equity awards granted prior to our IPO. All unvested awards granted pursuant to the MPK Coworker Incentive Plan II (the “MPK Plan”) vested in connection with the IPO as discussed further below in the section labeled "MPK II Units."
	-2	Includes pre-tax expense of $6.6 million in connection with the modification of Class B Common Unit awards granted pursuant to the CDW Holdings LLC 2007 Incentive Equity Plan to the Company’s former Chief Executive Officer, as discussed further below in the section labeled "Class B Common Units."
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	The weighted-average assumptions used to value the stock options granted during the years ended December 31, 2014 and 2013 are presented below.
			Year Ended December 31,
			2014				2013
	Weighted-average grant date fair value		$	7.23			$	4.75
	Weighted-average volatility (1)		30		%		35		%
	Weighted-average risk-free rate (2)		1.77		%		1.58		%
	Dividend yield		0.7		%		1		%
	Expected term (in years) (3)		6				5.4
	-1	Based upon an assessment of the two-year, five-year and implied volatility for the Company’s selected peer group, adjusted for the Company’s leverage.
	-2	Based on a composite U.S. Treasury rate.
	-3	Calculated using the simplified method. The simplified method 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 [Table Text Block]	The following table summarizes the Company's stock option activity for the year ended December 31, 2014:
	Options		Number of Options			Weighted-Average Exercise Price			Weighted-Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (millions)
	Outstanding at January 1, 2014		1,280,255			$17.00
	Granted		1,245,513			24.4
	Forfeited/Expired		(31,209	)		21.33
	Exercised		(73,487	)		17
	Outstanding at December 31, 2014		2,421,072			$20.75			8.3	$34.90
	Exercisable at December 31, 2014		576,963			$17.00			7.2	$10.50
	Vested and expected to vest at December 31, 2014		2,378,364			$20.74			8.3	$34.30
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]	The following table summarizes the Company's RSU activity for the year ended December 31, 2014:
		Number of Units			Weighted-Average Grant-Date Fair Value
	Nonvested at January 1, 2014	1,351,572			$	17.04
	Granted	25,895			24.29
	Vested/Settled	(5,984	)		17
	Forfeited	(126,781	)		17.04
	Nonvested at December 31, 2014	1,244,702			$	17.19
Schedule of Share-based Payment Award, Equity Investments other than Options, Valuation Assumptions [Table Text Block]	The following table summarizes the assumptions and resulting fair value of the Class B Common Unit grants for the years ended December 31, 2013 and 2012:
		Years Ended December 31,
	Assumptions	2013				2012
	Weighted-average grant date fair value	$	119			$	125.65
	Weighted-average volatility (1)	65.5		%		65.26		%
	Weighted-average risk-free rate (2)	0.18		%		0.19		%
	Dividend yield	0		%		0		%
	-1	Based upon an assessment of the two-year, five-year and implied volatility for the Company’s selected peer group, adjusted for the Company’s leverage.
	-2	Based on a composite U.S. Treasury rate.
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	The following table sets forth a summary of pre-IPO equity plan activity for the year ended December 31, 2013:
		Class B			MPK Plan
		Common Units			Units
	Outstanding at January 1, 2013	216,483			66,137
	Granted	400			—
	Forfeited	(860	)		(2,228	)
	Converted/Settled (1)	(216,023	)		(63,909	)
	Outstanding at December 31, 2013	—			—
	Vested at December 31, 2013	—			—
	-1	As discussed above, the Class B Common Units and MPK Plan Units were converted/settled into shares of the Company's common stock upon completion of the IPO. The converted Class B Common Units, to the extent unvested at the time of the IPO, relate to the grants of restricted stock disclosed above.

Earnings_per_Share_Tables

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares [Table Text Block]	The following is a reconciliation of basic shares to diluted shares:
		Years Ended December 31,
	(in millions)	2014	2013	2012
	Weighted-average shares - basic	170.6	156.6	145.1
	Effect of dilutive securities	2.2	2.1	0.7
	Weighted-average shares - diluted	172.8	158.7	145.8

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Revenue from External Customers by Products and Services [Table Text Block]	The following table presents net sales by major category for the years ended December 31, 2014, 2013 and 2012. Categories are based upon internal classifications. Amounts for the years ended December 31, 2013 and 2012 have been reclassified for certain changes in individual product classifications to conform to the presentation for the year ended December 31, 2014.
		Year Ended						Year Ended							Year Ended
		December 31, 2014						December 31, 2013							December 31, 2012
		Dollars in			Percentage			Dollars in				Percentage			Dollars in				Percentage
		Millions			of Total Net			Millions				of Total Net			Millions				of Total Net
					Sales							Sales							Sales
	Notebooks/Mobile Devices	$	2,352.30		19.5	%		$	1,698.40			15.8	%		$	1,462.80			14.4	%
	NetComm Products	1,615.90			13.4			1,486.30				13.8			1,351.50				13.3
	Enterprise and Data Storage (Including Drives)	1,024.30			8.5			999.2				9.3			981.5				9.7
	Other Hardware	4,549.20			37.6			4,178.50				38.8			4,075.70				40.3
	Software	2,076.70			17.2			1,993.10				18.5			1,877.70				18.5
	Services	371.4			3.1			332.7				3.1			285				2.8
	Other (1)	84.7			0.7			80.4				0.7			94				1
	Total net sales	$	12,074.50		100	%		$	10,768.60			100	%		$	10,128.20			100	%
	-1	Includes items such as delivery charges to customers and certain commission revenue.
Schedule of Segment Reporting Information, by Segment [Table Text Block]	The following table presents information about the Company’s segments for the years ended December 31, 2014, 2013 and 2012:
	(in millions)	Corporate			Public				Other				Headquarters				Total
	2014:00:00
	Net sales	$	6,475.50		$	4,879.40			$	719.6			$	—			$	12,074.50
	Income (loss) from operations	439.8			313.2				32.9				(112.9		)		673
	Depreciation and amortization expense	(96.3		)	(43.8		)		(8.8		)		(59.0		)		(207.9		)
	2013:00:00
	Net sales	$	5,960.10		$	4,164.50			$	644			$	—			$	10,768.60
	Income (loss) from operations(1)	363.3			246.5				27.2				(128.4		)		508.6
	Depreciation and amortization expense	(97.3		)	(44.0		)		(8.6		)		(58.3		)		(208.2		)
	2012:00:00
	Net sales	$	5,512.80		$	4,023.00			$	592.4			$	—			$	10,128.20
	Income (loss) from operations	349			246.7				18.6				(103.7		)		510.6
	Depreciation and amortization expense	(97.6		)	(44.0		)		(9.3		)		(59.3		)		(210.2		)
	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.

Supplemental_Guarantor_Informa1

Supplemental Guarantor Information (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Guarantor Information [Abstract]
Schedule of Condensed Cash Flow Statement [Table Text Block]	Condensed Consolidating Statement of Cash Flows
	Year Ended December 31, 2013
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Net cash (used in) provided by operating activities	$	(15.2	)	$	(130.3	)	$	508.8		$	5.5		$	—	$	(2.5	)	$	366.3
	Cash flows from investing activities:
	Capital expenditures	—			(40.8		)	(6.2		)	(0.1		)	—		—			(47.1		)
	Net cash used in investing activities	—			(40.8		)	(6.2		)	(0.1		)	—		—			(47.1		)
	Cash flows from financing activities:
	Proceeds from borrowings under revolving credit facility	—			63			—			—			—		—			63
	Repayments of borrowings under revolving credit facility	—			(63.0		)	—			—			—		—			(63.0		)
	Repayments of long-term debt	—			(51.1		)	—			—			—		—			(51.1		)
	Proceeds from issuance of long-term debt	—			1,535.20			—			—			—		—			1,535.20
	Payments to extinguish long-term debt	—			(2,047.4		)	—			—			—		—			(2,047.4		)
	Payment of debt financing costs	—			(6.1		)	—			—			—		—			(6.1		)
	Net change in accounts payable-inventory financing	—			—			7.4			—			—		—			7.4
	Payment of incentive compensation plan withholding taxes	—			(4.0		)	(19.6		)	(0.5		)	—		—			(24.1		)
	Net proceeds from issuance of common shares	424.7			—			—			—			—		—			424.7
	Dividends paid	(7.3		)	—			—			—			—		—			(7.3		)
	Advances to/from affiliates	(402.2		)	892.6			(490.4		)	—			—		—			—
	Other financing activities	—			0.4			—			—			—		—			0.4
	Net cash provided by (used in) financing activities	15.2			319.6			(502.6		)	(0.5		)	—		—			(168.3		)
	Effect of exchange rate changes on cash and cash equivalents	—			—			—			(0.7		)	—		—			(0.7		)
	Net increase in cash and cash equivalents	—			148.5			—			4.2			—		(2.5		)	150.2
	Cash and cash equivalents – beginning of period	—			48			—			9.8			—		(19.9		)	37.9
	Cash and cash equivalents – end of period	$	—		$	196.5		$	—		$	14		$	—	$	(22.4	)	$	188.1
	Condensed Consolidating Statement of Cash Flows
	Year Ended December 31, 2012
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Net cash (used in) provided by operating activities	$	—		$	(204.3	)	$	514.2		$	1.3		$	—	$	6.2		$	317.4
	Cash flows from investing activities:
	Capital expenditures	—			(27.0		)	(14.0		)	(0.4		)	—		—			(41.4		)
	Premium payments on interest rate cap agreements	—			(0.3		)	—			—			—		—			(0.3		)
	Net cash used in investing activities	—			(27.3		)	(14.0		)	(0.4		)	—		—			(41.7		)
	Cash flows from financing activities:
	Proceeds from borrowings under revolving credit facility	—			289			—			—			—		—			289
	Repayments of borrowings under revolving credit facility	—			(289.0		)	—			—			—		—			(289.0		)
	Repayments of long-term debt	—			(201.0		)	—			—			—		—			(201.0		)
	Proceeds from issuance of long-term debt	—			135.7			—			—			—		—			135.7
	Payments to extinguish long-term debt	—			(243.2		)	—			—			—		—			(243.2		)
	Payment of debt financing costs	—			(2.1		)	—			—			—		—			(2.1		)
	Net change in accounts payable-inventory financing	—			—			(29.5		)	—			—		—			(29.5		)
	Advances to/from affiliates	—			486			(486.5		)	0.5			—		—			—
	Other financing activities	—			2.1			—			—			—		—			2.1
	Net cash provided by (used in) financing activities	—			177.5			(516.0		)	0.5			—		—			(338.0		)
	Effect of exchange rate changes on cash and cash equivalents	—			—			—			0.3			—		—			0.3
	Net (decrease) increase in cash and cash equivalents	—			(54.1		)	(15.8		)	1.7			—		6.2			(62.0		)
	Cash and cash equivalents – beginning of period	—			102.1			15.8			8.1			—		(26.1		)	99.9
	Cash and cash equivalents – end of period	$	—		$	48		$	—		$	9.8		$	—	$	(19.9	)	$	37.9
	Condensed Consolidating Statement of Cash Flows
	Year Ended December 31, 2014
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Net cash (used in) provided by operating activities	$	—		$	(120.4	)	$	547.7		$	11.8		$	—	$	(4.1	)	$	435
	Cash flows from investing activities:
	Capital expenditures	—			(47.9		)	(7.1		)	—			—		—			(55.0		)
	Payment for equity investments	—			(86.8		)	—			—			—		—			(86.8		)
	Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	—			(20.9		)	—			—			—		—			(20.9		)
	Premium payments on interest rate cap agreements	—			(2.1		)	—			—			—		—			(2.1		)
	Net cash used in investing activities	—			(157.7		)	(7.1		)	—			—		—			(164.8		)
	Cash flows from financing activities:
	Repayments of long-term debt	—			(15.4		)	—			—			—		—			(15.4		)
	Proceeds from issuance of long-term debt	—			1,175.00			—			—			—		—			1,175.00
Payments to extinguish long-term debt	—			(1,299.0		)	—			—			—		—			(1,299.0		)
Payment of debt financing costs	—			(21.9		)	—			—			—		—			(21.9		)
Net change in accounts payable-inventory financing	—			—			75.5			—			—		—			75.5
Proceeds from stock option exercises	—			1.3			—			—			—		—			1.3
Proceeds from Coworker stock purchase plan	—			5.8			—			—			—		—			5.8
Dividends paid	(33.6		)	—			—			—			—		—			(33.6		)
Excess tax benefits from equity-based compensation	—			0.3			—			—			—		—			0.3
Advances to/from affiliates	33.6			581.9			(616.1		)	0.6			—		—			—
Net cash provided by (used in) financing activities	—			428			(540.6		)	0.6			—		—			(112.0		)
Effect of exchange rate changes on cash and cash equivalents	—			—			—			(1.8		)	—		—			(1.8		)
Net increase in cash and cash equivalents	—			149.9			—			10.6			—		(4.1		)	156.4
Cash and cash equivalents – beginning of period	—			196.5			—			14			—		(22.4		)	188.1
Cash and cash equivalents – end of period	$	—		$	346.4		$	—		$	24.6		$	—	$	(26.5	)	$	344.5
Schedule of Condensed Comprehensive Income (Loss) [Table Text Block]	Condensed Consolidating Statement of Comprehensive Income
	Year Ended December 31, 2014
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Comprehensive income	$	234.6		$	234.6		$	484.6		$	5.1		$	—	$	(724.3	)	$	234.6
	Condensed Consolidating Statement of Comprehensive Income
	Year Ended December 31, 2012
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Comprehensive income	$	121.5		$	121.5		$	322.8		$	13.2		$	—	$	(457.5	)	$	121.5
	Condensed Consolidating Statement of Comprehensive Income
	Year Ended December 31, 2013
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Comprehensive income	$	126.1		$	141.3		$	409		$	4.8		$	—	$	(555.1	)	$	126.1
Schedule of Condensed Balance Sheet [Table Text Block]	Condensed Consolidating Balance Sheet
	December 31, 2014
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Assets
	Current assets:
	Cash and cash equivalents	$	—		$	346.4		$	—		$	24.6		$	—	$	(26.5	)	$	344.5
	Accounts receivable, net	—			—			1,479.10			82			—		—			1,561.10
	Merchandise inventory	—			—			333.9			3.6			—		—			337.5
	Miscellaneous receivables	—			56.1			93.3			6.2			—		—			155.6
	Prepaid expenses and other	—			11			46			1.5			—		(3.8		)	54.7
	Total current assets	—			413.5			1,952.30			117.9			—		(30.3		)	2,453.40
	Property and equipment, net	—			80.5			55.5			1.2			—		—			137.2
	Equity investments	—			86.7			—			—			—		—			86.7
	Goodwill	—			751.8			1,439.00			26.8			—		—			2,217.60
	Other intangible assets, net	—			320			843.6			5.2			—		—			1,168.80
	Deferred financing costs, net	—			33			—			—			—		—			33
	Other assets	4.3			3.2			0.4			1.4			—		(6.1		)	3.2
	Investment in and advances to subsidiaries	932.2			2,784.50			—			—			—		(3,716.7		)	—
	Total assets	$	936.5		$	4,473.20		$	4,290.80		$	152.5		$	—	$	(3,753.1	)	$	6,099.90
	Liabilities and Shareholders’ Equity
	Current liabilities:
	Accounts payable-trade	$	—		$	23.9		$	671.9		$	34.7		$	—	$	(26.5	)	$	704
	Accounts payable-inventory financing	—			—			332.1			—			—		—			332.1
	Current maturities of long-term debt	—			15.4			—			—			—		—			15.4
	Deferred revenue	—			—			79.9			1.4			—		—			81.3
	Accrued expenses	—			137.8			193.6			7.9			—		(4.1		)	335.2
	Total current liabilities	—			177.1			1,277.50			44			—		(30.6		)	1,468.00
	Long-term liabilities:
	Debt	—			3,174.60			—			—			—		—			3,174.60
	Deferred income taxes	—			146.7			331.3			1.3			—		(4.3		)	475
	Other liabilities	—			42.6			3.7			1			—		(1.5		)	45.8
	Total long-term liabilities	—			3,363.90			335			2.3			—		(5.8		)	3,695.40
	Total shareholders’ equity	936.5			932.2			2,678.30			106.2			—		(3,716.7		)	936.5
	Total liabilities and shareholders' equity	$	936.5		$	4,473.20		$	4,290.80		$	152.5		$	—	$	(3,753.1	)	$	6,099.90
	Condensed Consolidating Balance Sheet
	December 31, 2013
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Assets
	Current assets:
	Cash and cash equivalents	$	—		$	196.5		$	—		$	14		$	—	$	(22.4	)	$	188.1
	Accounts receivable, net	—			—			1,375.90			75.1			—		—			1,451.00
	Merchandise inventory	—			—			378.9			3.1			—		—			382
	Miscellaneous receivables	—			49.9			91			5.4			—		—			146.3
	Prepaid expenses and other	—			10.7			33.4			5.1			—		(3.1		)	46.1
	Total current assets	—			257.1			1,879.20			102.7			—		(25.5		)	2,213.50
	Property and equipment, net	—			69.7			59.6			1.8			—		—			131.1
	Goodwill	—			751.9			1,439.00			29.4			—		—			2,220.30
	Other intangible assets, net	—			338.5			982.8			6.7			—		—			1,328.00
	Deferred financing costs, net	—			30.1			—			—			—		—			30.1
	Other assets	4.9			1.4			0.1			0.9			—		(5.7		)	1.6
	Investment in and advances to subsidiaries	706.8			2,909.40			—			—			—		(3,616.2		)	—
	Total assets	$	711.7		$	4,358.10		$	4,360.70		$	141.5		$	—	$	(3,647.4	)	$	5,924.60
	Liabilities and Shareholders' Equity
	Current liabilities:
	Accounts payable-trade	$	—		$	21.4		$	637.3		$	26.5		$	—	$	(22.4	)	$	662.8
	Accounts payable-inventory financing	—			—			256.6			—			—		—			256.6
	Current maturities of long-term debt	—			45.4			—			—			—		—			45.4
	Deferred revenue	—			—			89.9			4.9			—		—			94.8
	Accrued expenses	—			163.5			175.1			7.5			—		(3.1		)	343
	Total current liabilities	—			230.3			1,158.90			38.9			—		(25.5		)	1,402.60
	Long-term liabilities:
	Debt	—			3,205.80			—			—			—		—			3,205.80
Deferred income taxes	—			178.3			388.4			1.6			—		(4.8		)	563.5
Other liabilities	—			36.9			3.6			1.4			—		(0.9		)	41
Total long-term liabilities	—			3,421.00			392			3			—		(5.7		)	3,810.30
Total shareholders’ equity	711.7			706.8			2,809.80			99.6			—		(3,616.2		)	711.7
Total liabilities and shareholders’ equity	$	711.7		$	4,358.10		$	4,360.70		$	141.5		$	—	$	(3,647.4	)	$	5,924.60
Schedule of Condensed Income Statement [Table Text Block]	Consolidating Statement of Operations
	Year Ended December 31, 2014
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Net sales	$	—		$	—		$	11,542.30		$	532.2		$	—	$	—		$	12,074.50
	Cost of sales	—			—			9,684.90			468.3			—		—			10,153.20
	Gross profit	—			—			1,857.40			63.9			—		—			1,921.30
	Selling and administrative expenses	—			112.8			962.3			35.2			—		—			1,110.30
	Advertising expense	—			—			134			4			—		—			138
	(Loss) income from operations	—			(112.8		)	761.1			24.7			—		—			673
	Interest (expense) income, net	—			(197.7		)	0.1			0.3			—		—			(197.3		)
	Net loss on extinguishments of long-term debt	—			(90.7		)	—			—			—		—			(90.7		)
	Management fee	—			3.9			—			(3.9		)	—		—			—
	Other income, net	—			1.2			1.5			—			—		—			2.7
	(Loss) income before income taxes	—			(396.1		)	762.7			21.1			—		—			387.7
	Income tax benefit (expense)	—			141			(278.1		)	(5.7		)	—		—			(142.8		)
	(Loss) income before equity in earnings of subsidiaries	—			(255.1		)	484.6			15.4			—		—			244.9
	Equity in earnings of subsidiaries	244.9			500			—			—			—		(744.9		)	—
	Net income	$	244.9		$	244.9		$	484.6		$	15.4		$	—	$	(744.9	)	$	244.9
	Consolidating Statement of Operations
	Year Ended December 31, 2013
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Net sales	$	—		$	—		$	10,293.30		$	475.3		$	—	$	—		$	10,768.60
	Cost of sales	—			—			8,592.10			416.2			—		—			9,008.30
	Gross profit	—			—			1,701.20			59.1			—		—			1,760.30
	Selling and administrative expenses	24.4			103.9			957.3			35.3			—		—			1,120.90
	Advertising expense	—			—			126.8			4			—		—			130.8
	(Loss) income from operations	(24.4		)	(103.9		)	617.1			19.8			—		—			508.6
	Interest (expense) income, net	—			(250.6		)	0.2			0.3			—		—			(250.1		)
	Net loss on extinguishments of long-term debt	—			(64.0		)	—			—			—		—			(64.0		)
	Management fee	—			4.3			—			(4.3		)	—		—			—
	Other (expense) income, net	—			(0.5		)	1.2			0.3			—		—			1
	(Loss) income before income taxes	(24.4		)	(414.7		)	618.5			16.1			—		—			195.5
	Income tax benefit (expense)	9.2			142.2			(209.5		)	(4.6		)	—		—			(62.7		)
	(Loss) income before equity in earnings of subsidiaries	(15.2		)	(272.5		)	409			11.5			—		—			132.8
	Equity in earnings of subsidiaries	148			420.5			—			—			—		(568.5		)	—
	Net income	$	132.8		$	148		$	409		$	11.5		$	—	$	(568.5	)	$	132.8
	Consolidating Statement of Operations
	Year Ended December 31, 2012
	(in millions)	Parent			Subsidiary			Guarantor			Non-Guarantor			Co-Issuer		Consolidating			Consolidated
		Guarantor			Issuer			Subsidiaries			Subsidiary					Adjustments
	Net sales	$	—		$	—		$	9,683.00		$	445.2		$	—	$	—		$	10,128.20
	Cost of sales	—			—			8,071.50			387.1			—		—			8,458.60
	Gross profit	—			—			1,611.50			58.1			—		—			1,669.60
	Selling and administrative expenses	—			103.7			891.6			34.2			—		—			1,029.50
	Advertising expense	—			—			125.1			4.4			—		—			129.5
	(Loss) income from operations	—			(103.7		)	594.8			19.5			—		—			510.6
	Interest (expense) income, net	—			(308.0		)	0.4			0.2			—		—			(307.4		)
	Net loss on extinguishments of long-term debt	—			(17.2		)	—			—			—		—			(17.2		)
	Management fee	—			3.8			—			(3.8		)	—		—			—
	Other income (expense), net	—			—			0.2			(0.1		)	—		—			0.1
	(Loss) income before income taxes	—			(425.1		)	595.4			15.8			—		—			186.1
	Income tax benefit (expense)	—			210.6			(272.6		)	(5.1		)	—		—			(67.1		)
	(Loss) income before equity in earnings of subsidiaries	—			(214.5		)	322.8			10.7			—		—			119
	Equity in earnings of subsidiaries	119			333.5			—			—			—		(452.5		)	—
	Net income	$	119		$	119		$	322.8		$	10.7		$	—	$	(452.5	)	$	119

Description_Of_Business_And_Su3

Description Of Business And Summary Of Significant Accounting Policies Property Plant and Equipment (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Asset Retirement Obligation	0.5	$0.50
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	5B toB 10B years
Building and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	5 to 25 years
Computer and Data Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 to 5 years
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 to 5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	5 to 10 years

Description_Of_Business_And_Su4

Description Of Business And Summary Of Significant Accounting Policies Goodwill and Other Intangible Assets (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$0	$0	$0
Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	$0	$0	$0
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite Lived Intangible Assets, Estimated Useful Lives	11B toB 14B years
Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Finite Lived Intangible Assets, Estimated Useful Lives	20 years
Internally Developed Software [Member]
Finite-Lived Intangible Assets [Line Items]
Finite Lived Intangible Assets, Estimated Useful Lives	3 to 5 years
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite Lived Intangible Assets, Estimated Useful Lives	1 to 10 years

Description_Of_Business_And_Su5

Description Of Business And Summary Of Significant Accounting Policies Accumulated Other Comprehensive Loss (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	($16.60)	($6.30)	$0.40
Accumulated Other Comprehensive Income (Loss), Net of Tax	($16.60)	($6.30)	$0.40

Property_And_Equipment_Details

Property And Equipment (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Land	$27.70	$27.70
Machinery and equipment	54.3	53
Building and leasehold improvements	105.1	104.8
Computer and data processing equipment	65.6	61.2
Capitalized Computer Software, Gross	10.6	30.9
Furniture and fixtures	21.7	21.6
Construction in progress	24.7	10.9
Total property and equipment	309.7	310.1
Less accumulated depreciation	172.5	179
Net property and equipment	137.2	131.1
Property, Plant and Equipment, Disposals	32	7.9	12.2
Pre-tax loss	0.1	0	0.1
Depreciation expense	$25.80	$27.20	$32

Goodwill_And_Other_Intangible_2

Goodwill And Other Intangible Assets Goodwill and Intangible Assets, Test for Impairment (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 01, 2014	Dec. 01, 2013	Dec. 01, 2012
Goodwill [Line Items]
Number of Reportable Segments	2
Number of operating segments which do not meet reporting unit quantitative threshold	3
Goodwill Impairment Test, Income Approach Weight		75.00%	75.00%	75.00%
Goodwill Impairment Test, Market Approach Weight		25.00%	25.00%	25.00%
Years Forecasted in Goodwill Impairment Income Approach		6	6	6
Long-Term Consolidated Annual Growth Rate		3.50%	3.50%	3.50%
Corporate Reporting Unit [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		169.00%	107.00%	49.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.00%	10.00%	11.50%
Public Segment Reporting Unit [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		147.00%	82.00%	44.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.00%	10.00%	11.50%
Canada Operating Segment [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		276.00%	167.00%	104.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.30%	10.30%	11.80%
CDW Advanced Services Operating Segment [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		78.00%	168.00%	17.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		11.50%	10.50%	12.00%

Schedule_of_Goodwill_by_Segmen

Schedule of Goodwill by Segment (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Goodwill [Roll Forward]
Goodwill, Gross	$4,174.10		$4,163.10
Period Increase (Decrease)	-2.7		11
Translation adjustment	-2.7		-2.1
Contingent consideration related to pre-2009 business combination			13.1	[1]
Goodwill, Gross	4,171.40		4,174.10
Accumulated impairment charges	-1,953.80		-1,953.80		-1,953.80
Goodwill	2,217.60		2,220.30		2,209.30
Corporate [Member]
Goodwill [Roll Forward]
Goodwill, Gross	2,803.20		2,794.40
Period Increase (Decrease)	0		8.8
Translation adjustment	0		0
Contingent consideration related to pre-2009 business combination			8.8	[1]
Goodwill, Gross	2,803.20		2,803.20
Accumulated impairment charges	-1,571.40		-1,571.40		-1,571.40
Goodwill	1,231.80		1,231.80		1,223
Public [Member]
Goodwill [Roll Forward]
Goodwill, Gross	1,265.40		1,261.40
Period Increase (Decrease)	0		4
Translation adjustment	0		0
Contingent consideration related to pre-2009 business combination			4	[1]
Goodwill, Gross	1,265.40		1,265.40
Accumulated impairment charges	-354.1		-354.1		-354.1
Goodwill	911.3		911.3		907.3
Other Segments [Member]
Goodwill [Roll Forward]
Goodwill, Gross	105.5	[2]	107.3	[2]
Period Increase (Decrease)	-2.7	[2]	-1.8	[2]
Translation adjustment	-2.7	[2]	-2.1	[2]
Contingent consideration related to pre-2009 business combination			0.3	[1],[2]
Goodwill, Gross	102.8	[2]	105.5	[2]
Accumulated impairment charges	-28.3	[2]	-28.3	[2]	-28.3	[2]
Goodwill	74.5	[2]	77.2	[2]	79	[2]
Kelway Operating Segment [Member]
Goodwill [Roll Forward]
Goodwill	$0		$0		$0
[1]	During 2013, the Company recorded a $13.1 million net-of-tax addition to goodwill in connection with the settlement of the MPK Coworker Incentive Plan II and related charitable contribution. The charitable contribution was accounted for as additional purchase price (goodwill) in accordance with pre-2009 business combinations accounting guidance. See Note 10 for additional discussion of this transaction.
[2]	Other is comprised of CDW Advanced Services, Canada, and Kelway reporting units. There is no goodwill attributable to the Kelway reporting unit.

Intangible_Assets_by_Asset_Typ

Intangible Assets by Asset Type (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets [Line Items]
Gross Carrying Amount	$2,394	$2,413.40
Accumulated Amortization	1,225.20	1,085.40
Net Carrying Amount	1,168.80	1,328
Customer Relationships [Member]
Intangible Assets [Line Items]
Gross Carrying Amount	1,859.70	1,860.80
Accumulated Amortization	1,012.10	872.8
Net Carrying Amount	847.6	988
Trade Name [Member]
Intangible Assets [Line Items]
Gross Carrying Amount	421	421
Accumulated Amortization	152	130.9
Net Carrying Amount	269	290.1
Internally Developed Software [Member]
Intangible Assets [Line Items]
Gross Carrying Amount	110.1	128.5
Accumulated Amortization	58.9	79.8
Net Carrying Amount	51.2	48.7
Disposal of Fully Amortized Definite-Lived Intangible Assets	41.7	0
Other Intangible Assets [Member]
Intangible Assets [Line Items]
Gross Carrying Amount	3.2	3.1
Accumulated Amortization	2.2	1.9
Net Carrying Amount	$1	$1.20

Amortization_of_Intangible_Ass

Amortization of Intangible Assets (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of Intangible Assets	$182.10	$181	$178.20
Amortization Expense 2015	180.7
Amortization Expense 2016	172.8
Amortization Expense 2017	167.1
Amortization Expense 2018	160.4
Amortization Expense 2019	$158.90

Inventory_Financing_Agreements2

Inventory Financing Agreements (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Inventory Financing Agreements [Line Items]
Accounts Payable Inventory Financing	$332.10	$256.60
Accounts Payable, Inventory Financing [Member]
Inventory Financing Agreements [Line Items]
Revolving Loan financing agreement	330.1	256.1
Other inventory financing agreements	2	0.5
Accounts Payable Inventory Financing	332.1	256.6
Previous Revolving Credit Facility [Member] | Accounts Payable, Inventory Financing [Member]
Inventory Financing Agreements [Line Items]
Floorplan sub-facility	$400

Operating_Leases_Details

Operating Leases (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2013	$19.10
2014	15.3
2015	16.1
2016	13.6
2017	12.8
Thereafter	50.6
Total future minimum lease payments	127.5	[1]
Operating Leases, Rent Expense, Net [Abstract]
Operating Leases, Rent Expense	$21.40		$20.70	$22.40
[1]	(1) Included in these amounts are future minimum lease payments commencing in the fourth quarter of 2016 that relate to a new lease entered into in December 2014 for the Companybs future headquarters in Lincolnshire, Illinois. Also reflected in these amounts is the future expiration of two leases in the first quarter of 2016 for facilities currently in use by the Company which the Company plans to consolidate into the new headquarters location and accordingly, these leases will not be renewed.

LongTerm_Debt_Debt_Balances_an

Long-Term Debt Debt Balances and Interest Rates (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013	Jul. 31, 2013	Apr. 29, 2013
In Millions, unless otherwise specified
Debt Instrument [Line Items]
Net Income free of restrictions under credit agreements	$230.30
Debt, long-term and short-term	3,192.40
Debt, total long-term and short-term	3,190		3,251.20
Current maturities of long-term debt	-15.4		-45.4
Debt	3,174.60		3,205.80
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.00%	[1]
Debt, long-term and short-term	0		0
Term Loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	3.25%	[1]
Debt, long-term and short-term	1,513.50		1,528.90
Debt Instrument, Unamortized Discount	-3.7		-4.4	1.4	3.4
Senior secured notes due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.00%	[1]
Debt, long-term and short-term	0		325
Senior notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	8.50%	[1]
Debt, long-term and short-term	503.9		1,305
Premium, Unamortized	1.3		4.2
Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	6.00%	[1]
Debt, long-term and short-term	600
Premium, Unamortized			0
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	5.50%	[1]
Debt, long-term and short-term	575
Premium, Unamortized			0
Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	0.00%	[1]
Debt, long-term and short-term	$0		$92.50
[1]	Interest rate at DecemberB 31, 2014.

LongTerm_Debt_Revolving_Loan_D

Long-Term Debt Revolving Loan (Details) (USD $)	12 Months Ended			3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Sep. 30, 2014	Jul. 31, 2013
Debt Instrument [Line Items]
Debt, long-term and short-term	$3,192,400,000			$3,192,400,000
Gains (Losses) on Extinguishment of Debt	90,700,000	64,000,000	17,200,000
Deferred Finance Costs, Noncurrent, Net	33,000,000	30,100,000	53,200,000	33,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term	0	0		0
Letters of Credit Outstanding, Amount	2,100,000			2,100,000
Floorplan sub-facility, reserve	312,300,000			312,300,000
Line of Credit Facility, Maximum Borrowing Capacity	1,250,000,000			1,250,000,000
Line of Credit Facility, Fee on Unused Portion, Basis Points	25			25
Line of Credit Facility, Decrease in Applicable Interest Rate Margin, Basis Points					50
Gains (Losses) on Extinguishment of Debt	400,000
Deferred Finance Costs, Noncurrent, Net	6,400,000			6,400,000
Variable Interest Rate Margin, ABR Determination, Basis Point Plus Federal Funds Effective Rate	50			50
Variable Interest Rate Margin, ABR Determination, Percentage Plus LIBOR	1.00%			1.00%
Potential Margin Reduction	0.25%			0.25%
Line of Credit Facility, Borrowing Base	1,253,400,000			1,253,400,000
Line of Credit Facility, Remaining Borrowing Capacity	935,600,000			935,600,000
Revolving Loan, Consecutive Business Days Below Minimum Average Daily Excess Cash Availability Requirement	5 days
Revolving Loan, Minimum Average Daily Excess Cash Availability Requirement, Consecutive Business Days Met	30 days
Line Of Credit Facility, Maximum Aggregate Increase	300,000,000			300,000,000
Revolving Loan Maturity Acceleration Provision, Days Prior to Maturity				45 days
Revolving Loan Maturity Acceleration Provision, Excess Cash Availability Limit, Amount Plus Maturing Debt	150,000,000			150,000,000
Minimum Liquidity Condition, Cash Availability	125,000,000			125,000,000
Cash Availability, Percentage of Borrowing Base	10.00%			10.00%
Minimum Liquidity Condition, Amount	100,000,000			100,000,000
Fixed Charge Coverage Ratio	1			1
Previous Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	900,000,000			900,000,000
Line Of Credit Facility, Maximum Aggregate Increase	200,000,000			200,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term	1,513,500,000	1,528,900,000		1,513,500,000
Gains (Losses) on Extinguishment of Debt		10,300,000
Deferred Finance Costs, Net						6,100,000
Higher Utilization [Member] | Previous Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Fee on Unused Portion, Basis Points	37.5			37.5
Lower Utilization [Member] | Previous Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Fee on Unused Portion, Basis Points	50			50
LIBOR [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.50%			1.50%
LIBOR [Member] | Minimum [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.25%			2.25%
LIBOR [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.00%			2.00%
LIBOR [Member] | Maximum [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.50%			2.50%
ABR [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	0.50%			0.50%
ABR [Member] | Minimum [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.25%			1.25%
ABR [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.00%			1.00%
ABR [Member] | Maximum [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.50%			1.50%
Accounts Payable, Inventory Financing [Member]
Debt Instrument [Line Items]
Revolving Loan financing agreement	330,100,000	256,100,000		330,100,000
Accounts Payable, Inventory Financing [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Amount owed under Revolving loan financing agreement	312,300,000			312,300,000
Floorplan sub-facility, variation in balance due to timing	17,800,000			17,800,000
Accounts Payable, Inventory Financing [Member] | Previous Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Floorplan sub-facility	$400,000,000			$400,000,000
Percentage reserve for open orders under financing agreement					15.00%

LongTerm_Debt_Term_Loan_Detail

Long-Term Debt Term Loan (Details) (USD $)	12 Months Ended				1 Months Ended		9 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Jul. 31, 2013	Apr. 30, 2013	Sep. 30, 2013	Apr. 29, 2013	Mar. 31, 2015
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt	$1,175,000,000		$1,535,200,000	$135,700,000
Deferred financing costs, net	33,000,000		30,100,000	53,200,000
Debt, long-term and short-term	3,192,400,000
Gains (Losses) on Extinguishment of Debt	90,700,000		64,000,000	17,200,000
Write off of Deferred Debt Issuance Cost	12,600,000		20,100,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Fee on Unused Portion, Basis Points	25
Deferred financing costs, net	6,400,000
Debt, long-term and short-term	0		0
Long-term Debt, Weighted Average Interest Rate	0.00%	[1]
Gains (Losses) on Extinguishment of Debt	400,000
Term Loan [Member]
Debt Instrument [Line Items]
Proceeds from issuance of long-term debt						1,350,000,000
Discount, percent of par					99.25%			99.75%
Debt Instrument, Unamortized Discount	-3,700,000		-4,400,000		1,400,000			3,400,000
Deferred Finance Costs, Net					6,100,000
Debt, long-term and short-term	1,513,500,000		1,528,900,000
Long-term Debt, Weighted Average Interest Rate	3.25%	[1]
Gains (Losses) on Extinguishment of Debt			10,300,000
Debt Instrument, Face Amount					190,000,000
Net leverage ratio	3.1
Quarterly amortization payment of original principal, Percent	0.25%
Term Loan [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate	3.25%
Prior Term Loan Facility [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term								1,299,500,000
Term Loan, Repayments							40,000,000
Minimum [Member] | Revolving Credit Facility [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	0.50%
Minimum [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.50%
Minimum [Member] | Term Loan [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.25%
Minimum [Member] | Term Loan [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.25%
Reference Interest Rate Floor	1.00%
Maximum [Member] | Revolving Credit Facility [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.00%
Maximum [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.00%
Maximum [Member] | Term Loan [Member] | ABR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	1.50%
Maximum [Member] | Term Loan [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Variable Interest Rate Margin	2.50%
Cap agreement effective January 14, 2013-2015 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	1,150,000,000
Derivative, Cap Interest Rate	2.40%
Derivative Asset, Noncurrent	0
Cap agreement effective January 14, 2015-2017 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	1,000,000,000
Derivative Asset, Noncurrent	1,700,000
Subsequent Event [Member] | Cap agreement effective January 14, 2015-2017 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount									$400,000,000
Derivative, Cap Interest Rate									2.00%
[1]	Interest rate at DecemberB 31, 2014.

LongTerm_Debt_Interest_Rate_Ca

Long-Term Debt Interest Rate Caps (Details) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Cap agreement effective January 14, 2013-2015 [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held	10
Derivative Asset, Noncurrent	$0
Derivative, Notional Amount	1,150
Derivative, Cap Interest Rate	2.40%
Cap agreement effective January 14, 2015-2017 [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held	14
Derivative Asset, Noncurrent	1.7
Derivative, Notional Amount	$1,000

LongTerm_Debt_Senior_Secured_N

Long-Term Debt Senior Secured Notes (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 05, 2014	Jul. 02, 2013
Debt Instrument [Line Items]
Debt, long-term and short-term	$3,192.40
Gains (Losses) on Extinguishment of Debt	90.7	64	17.2
Write off of Deferred Debt Issuance Cost	12.6	20.1
Senior secured notes due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	8.00%
Debt, long-term and short-term	0	325
Debt Instrument, Repurchased Face Amount				325	175
Redemption Premium, percentage of par value				106.06%	108.00%
Extinguishment of Debt, Accrued Interest Paid to Lenders					0.7
Gains (Losses) on Extinguishment of Debt	-23.7	16.7
Extinguishment of Debt, Fees Paid to Lenders	13	14
Extinguishment of Debt, Make-whole Interest Payment	6.7
Write off of Deferred Debt Issuance Cost	$4	$2.70

LongTerm_Debt_Senior_Notes_due

Long-Term Debt Senior Notes due 2015 (Details) (USD $)	12 Months Ended			3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Mar. 31, 2014	Sep. 30, 2014	Dec. 01, 2014	Aug. 05, 2014	Mar. 20, 2014
Debt Instrument [Line Items]
Debt, long-term and short-term	$3,192.40			$3,192.40
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Gains (Losses) on Extinguishment of Debt	90.7	64	17.2
Write off of Deferred Debt Issuance Cost	12.6	20.1
Deferred financing costs, net	33	30.1	53.2	33
Senior notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	8.50%			8.50%
Debt, long-term and short-term	503.9	1,305		503.9
Senior Notes, Amount Repurchased							541.4	234.7	25
Extinguishment of Debt, Fees Paid to Lenders	23			10	2.4
Extinguishment of Debt, Accrued Interest Paid to Lenders									1
Gains (Losses) on Extinguishment of Debt	-36.9			-22.1		-2.7
Write off of Deferred Debt Issuance Cost	$4.70			$2.20	$0.30

LongTerm_Debt_Senior_Notes_Det

Long-Term Debt Senior Notes (Details) (USD $)	12 Months Ended			3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Mar. 31, 2014	Sep. 30, 2014	Dec. 01, 2014	Aug. 05, 2014	Mar. 20, 2014
Debt Instrument [Line Items]
Payments for Derivative Instrument, Investing Activities	$2.10	$0	$0.30
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Debt, long-term and short-term	3,192.40			3,192.40
Deferred financing costs, net	33	30.1	53.2	33
Gains (Losses) on Extinguishment of Debt	-90.7	-64	-17.2
Write off of Deferred Debt Issuance Cost	12.6	20.1
Senior notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	8.50%			8.50%
Redemption Premium, percentage of par value							106.20%	108.76%	109.75%
Extinguishment of Debt, Accrued Interest Paid to Lenders									1
Debt, long-term and short-term	503.9	1,305		503.9
Premium, Unamortized	1.3	4.2		1.3
Debt Instrument, Repurchased Face Amount							541.4	234.7	25
Gains (Losses) on Extinguishment of Debt	36.9			22.1		2.7
Write off of Deferred Debt Issuance Cost	4.7			2.2	0.3
Extinguishment of Debt, Fees Paid to Lenders	23			10	2.4
Extinguishment of Debt, Make-whole Interest Payment	10.6			10.6
Write off of Deferred Debt issuance Cost, unamortized premium	1.4			0.7
Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	6.00%			6.00%
Debt, long-term and short-term	600			600
Premium, Unamortized		0
Deferred financing costs, net	8			8
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	5.50%			5.50%
Debt, long-term and short-term	575			575
Premium, Unamortized		0
Deferred financing costs, net	7.5			7.5
Cap agreement effective January 14, 2015-2017 [Member]
Debt Instrument [Line Items]
Payments for Derivative Instrument, Investing Activities	2.1
Derivative Asset, Noncurrent	1.7			1.7
Derivative, Notional Amount	$1,000			$1,000

LongTerm_Debt_Senior_Subordina

Long-Term Debt Senior Subordinated Notes (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended			1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 08, 2013	Feb. 28, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jul. 31, 2013	Apr. 30, 2013	Jul. 02, 2013	9-May-14	Feb. 21, 2014	Jan. 22, 2014	Oct. 18, 2013	Aug. 01, 2013	Mar. 10, 2010	Sep. 30, 2014
Debt Instrument [Line Items]
Debt, long-term and short-term	$3,192.40
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Proceeds from exercise in full of overallotment option											56
Gains (Losses) on Extinguishment of Debt	90.7	64	17.2
Write off of Deferred Debt Issuance Cost	12.6	20.1
Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate	12.54%
Debt, long-term and short-term	0	92.5					92.5
Debt Instrument, Repurchased Face Amount				50		50						42.5	20	30	155	324	28.5
Redemption Premium, percentage of par value				106.27%								104.18%	104.18%		104.18%	106.27%
Gains (Losses) on Extinguishment of Debt	-2.2			3.9		2.7	8.5	24.6
Extinguishment of Debt, Fees Paid to Lenders	1.8			3.1		2.1	6.5	20.3
Write off of Deferred Debt Issuance Cost	0.4			0.8	0.6		2	4.3
Extinguishment of Debt, Accrued Interest Paid to Lenders				2.5								0.4	1.9		0.2	12
Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term																		0
Term Loan [Member]
Debt Instrument [Line Items]
Debt, long-term and short-term	1,513.50	1,528.90					1,528.90
Debt Instrument, Face Amount									190
Proceeds from issuance of long-term debt										1,350
Gains (Losses) on Extinguishment of Debt		10.3
IPO Proceeds [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount																146
Term Loan Incremental Borrowings [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount																$178

LongTerm_Debt_LongTerm_Debt_Ma

Long-Term Debt Long-Term Debt Maturities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Long-term Debt, Unclassified [Abstract]
Current maturities of long-term debt	$15.40	$45.40
Long-term Debt Maturity, Repayments of Principal in Year Two	0
Long-term Debt Maturity, Repayments of Principal in Year Three	0
Long-term Debt Maturity, Repayments of Principal in Year Four	0
Long-term Debt Maturity, Repayments of Principal in Year Five	503.9
Long-term Debt Maturity, Repayments of Principal after Year Five	2,673.10
Debt, total long-term and short-term	$3,192.40

LongTerm_Debt_Fair_Value_of_Lo

Long-Term Debt Fair Value of Long-Term Debt (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, long-term and short-term	$3,192.40
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, fair value disclosure	3,208.70
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, long-term and short-term	3,192.40
Senior notes due 2019 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, long-term and short-term	503.9	1,305
Premium, Unamortized	$1.30	$4.20

LongTerm_Debt_Deferred_Financi

Long-Term Debt Deferred Financing Costs (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred Financing Costs [Roll Forward]
Deferred financing costs, net	$30.10	$53.20
Increase in Deferred Finance Costs	21.9	6.1
Amortization of Financing Costs	6.4	9.1
Write off of Deferred Debt Issuance Cost	-12.6	-20.1
Deferred financing costs, net	$33	$30.10
Weighted Average Remaining Life, Deferred Finance Costs	6 years 7 months 9 days	4 years 11 months 7 days

Income_Taxes_Details

Income Taxes (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Undistributed Earnings of Foreign Subsidiaries	$66.60
Income (loss) before income taxes [Abstract]
Domestic	366.6	179.4	170.3
Foreign	21.1	16.1	15.8
Income (loss) before income taxes	387.7	195.5	186.1
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	124
Tax Credit Carryforward, Amount	$19.60

Income_Taxes_Income_Tax_Expens

Income Taxes Income Tax Expense by Component (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current Income Tax Expense (Benefit) [Abstract]
Federal	$206.80	$96.70	$110.30
State	19.3	10.1	8
Foreign	5.8	4.6	5.1
Total current	231.9	111.4	123.4
Deferred Income Tax Expense (Benefit) [Abstract]
Domestic	-89	-48.6	-56.2
Foreign	-0.1	-0.1	-0.1
Total deferred	-89.1	-48.7	-56.3
Income tax expense	$142.80	$62.70	$67.10

Income_Taxes_Effective_Tax_Rat

Income Taxes Effective Tax Rate Reconciliation (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$135.70	$68.40	$65.10
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	35.00%	35.00%	35.00%
State Income Taxes, net of federal effect	6.5	-5	0.4
Effective Income Tax Rate Reconciliation, State Income Taxes, net of federal effect	1.60%	-2.60%	0.20%
Income Tax Reconciliation, Share-based Compensation Cost	1.1	1.5	5.7
Effective Income Tax Rate Reconciliation, Share-based Compensation Cost	0.30%	0.70%	3.10%
Income Tax Reconciliation, Effect of rates different than statutory	-1.9	-1.4	-1.4
Effective Income Tax Rate Reconciliation, Effect fo rates different than statutory	-0.50%	-0.70%	-0.80%
Income Tax Reconciliation, Other Adjustments	1.4	-0.8	-2.7
Effective Income Tax Rate Reconciliation, Other Adjustments	0.40%	-0.30%	-1.50%
Income tax expense	$142.80	$62.70	$67.10
Effective Income Tax Rate	36.80%	32.10%	36.00%

Income_Taxes_Deferred_Tax_Asse

Income Taxes Deferred Tax Assets and Liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Deferred Tax Assets, Gross [Abstract]
Deferred interest	$32.90	$43.50
State net operating loss and credit carryforwards, net	18.8	21.1
Payroll and benefits	27	16.2
Deferred Tax Assets, Rent	5.5	6.4
Accounts receivable	6.3	5.4
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	6.5	1.6
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other	1.5	1.5
Other	5	7.1
Total deferred tax assets	103.5	102.8
Deferred Tax Liabilities, Gross [Abstract]
Software and intangibles	425.3	486.2
Deferred Income	116.2	145.5
Property and equipment	22.5	25
Other	15.3	11.6
Total deferred tax liabilites	579.3	668.3
Deferred tax assets valuation allowance	0	0
Net deferred tax liabilities	475.8	565.5
Operating Loss Carryforwards [Line Items]
Undistributed Earnings of Foreign Subsidiaries	66.6
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	124
Tax Credit Carryforward, Amount	$19.60

Income_Taxes_Rollforward_of_Un

Income Taxes Rollforward of Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits	$0		$0	$0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$0	$0

Shareholders_Equity_Details

Shareholders' Equity (Details) (USD $)	1 Months Ended	2 Months Ended	3 Months Ended												12 Months Ended					1 Months Ended
	Jun. 30, 2013	Feb. 26, 2015	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Jul. 31, 2013	Nov. 06, 2014	Jul. 02, 2013
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount																					$500,000,000
Stock Repurchased During Period, Shares		0
Other IPO Related Expenses																	2,400,000	[1]
Employee Stock Purchase Plan, discount to market price, percent															5.00%
Equity-based compensation expense															16,400,000		46,600,000		22,100,000
Proceeds from shares sold by certain selling stockholders															0
Preferred Stock, Shares Issued			0								0				0		0
Secondary-offering related expenses			200,000		300,000		500,000		400,000						1,400,000	[1]	600,000
Proceeds from Issuance Initial Public Offering																	424,700,000
Stockholders' Equity Note, Stock Split, Conversion Ratio	143.0299613
Common Stock, Par Value			$0.01								$0.01				$0.01		$0.01
Preferred Stock, Shares Authorized			100,000,000								100,000,000				100,000,000		100,000,000
Preferred Stock, Par or Stated Value Per Share			$0.01								$0.01				$0.01		$0.01
Preferred Stock, Shares Outstanding			0								0				0		0
Common Stock, Shares Authorized			1,000,000,000								1,000,000,000				1,000,000,000		1,000,000,000
Common Stock, Dividends, Per Share, Cash Paid			$0.07		$0.04		$0.04		$0.04		$0.04	$0	$0	$0
Dividends, Common Stock, Cash			11,700,000		7,300,000		7,300,000		7,300,000		7,300,000	0	0	0
Coworker Stock Purchase Plan [Member]
Class of Stock [Line Items]
Equity-based compensation expense															$0
IPO [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues																				23,250,000
Share Price																						$17
IPO Over-allotment [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues																	3,487,500
Secondary Offering [Member]
Class of Stock [Line Items]
Shares sold by certain selling stockholders			15,000,000		15,000,000		15,000,000		10,000,000								15,000,000
Secondary offering over-allotment [Member]
Class of Stock [Line Items]
Shares sold by certain selling stockholders			2,250,000	[2]	0	[2],[3]	2,250,000	[2]	1,500,000	[2]							2,250,000	[2]
[1]	Other expenses include secondary-offering expenses of $1.4 million and $0.6 million for the years ended December 31, 2014 and 2013, respectively.
[2]	Under each underwriting agreement, the selling stockholders granted the underwriters an option, exercisable for thirty days, to purchase up to the additional amount of shares noted.
[3]	The option to purchase additional shares was not exercised in connection with the September 2014 secondary offering

Shareholders_Equity_IPO_and_se

Shareholders' Equity IPO- and secondary-offering related expenses (Details) (USD $)	3 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2014		Dec. 31, 2013
Class of Stock [Line Items]
Secondary-offering related expenses	$0.20	$0.30	$0.50	$0.40	$1.40	[1]	$0.60
Net proceeds used for termination of management services agreement					0	[2]	24.4	[2]
Other IPO Related Expenses							2.4	[1]
IPO and Secondary-offering related expenses							75
Accelerated share based compensation expense and related employer payroll taxes					0	[3]	40.7	[3]
Charge for payment of RDU Plan cash retention pool					0	[4]	7.5	[4]
Net proceeds used for termination of Management Services Agreement							$24.40
[1]	Other expenses include secondary-offering expenses of $1.4 million and $0.6 million for the years ended December 31, 2014 and 2013, respectively.
[2]	Represents the payment of a termination fee to affiliates of the Sponsors in connection with the termination of the management services agreement with such entities.
[3]	See Note 10 for additional discussion of the impact of the IPO on the Company's equity awards.
[4]	See Note 12 for additional discussion of this transaction.

EquityBased_Compensation_Detai

Equity-Based Compensation (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2007
Equity-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$1,000,000	$0
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Accelerated share based compensation expense recognized		36,700,000
Payment of incentive compensation plan withholding taxes related to the acceleration of share vesting		24,000,000
Payment of incentive compensation plan withholding taxes, employer portion		4,000,000
Accrued contingent consideration		20,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, beginning number	1,280,255
Options outstanding, beginning weighted-average exercise price	$17
Options, Grants in Period, Gross	1,245,513
Options, Grants in Period, Weighted Average Exercise Price	$24.40
Options, Forfeitures and Expirations in Period	-31,209
Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$21.33
Options, Exercises in Period	73,487
Options, Exercises in Period, Weighted Average Exercise Price	$17
Options outstanding, ending number	2,421,072	1,280,255
Options outstanding, ending weighted-average exercise price	$20.75	$17
Options, Outstanding, Weighted Average Remaining Contractual Term	8 years 3 months 21 days
Options, Outstanding, Intrinsic Value	34,900,000
Options, Exercisable, Number	576,963
Options, Exercisable, Weighted Average Exercise Price	$17
Options, Exercisable, Weighted Average Remaining Contractual Term	7 years 2 months 26 days
Options, Exercisable, Intrinsic Value	10,500,000
Options, Vested and Expected to Vest, Outstanding, Number	2,378,364
Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$20.74
Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	8 years 3 months 19 days
Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	34,300,000
Equity-based compensation [Abstract]
Equity-based compensation expense	16,400,000	46,600,000	22,100,000
Equity-based Compensation Expense, Tax Benefit from Compensation Expense	-5,100,000	-16,500,000	-2,300,000
Allocated Share-based Compensation Expense, Net of Tax	11,300,000	30,100,000	19,800,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized [Abstract]
Equity-based Compensation Expense Not yet Recognized	28,900,000
Equity-based Compensation Expense Not yet Recognized, Period for Recognition	2 years 3 months 5 days
Stock Option Contractual Life	10 years 0 months 0 days
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years 0 months 0 days
Equity-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Options, Grants in Period, Weighted Average Grant Date Fair Value	$7.23	$4.75
Weighted-Average Volatility	30.00%	35.00%
Weighted-Average Risk-Free Rate	1.77%	1.58%
Dividend Yield	0.70%	1.00%
Fair Value Assumptions, Expected Term	6 years 0 months 0 days	5 years 5 months 0 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments Other than Options, Nonvested, Number	260,514
Equity Instruments Other Than Options, Vested in Period	-2,321,973
Equity Instruments Other than Options, Vested in Period, Fair Value	68,600,000	26,700,000
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Awards Granted		3,798,508
Equity Awards Forfeited	-9,546
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments Other than Options, Nonvested, Number	1,244,702	1,351,572
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$24.29	$17.03
Equity Instruments Other Than Options, Vested in Period	-5,984
Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$17
Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$17.04
Equity Instruments Other than Options, Vested in Period, Fair Value	200,000	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$17.19	$17.04
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Awards Granted	25,895
Equity Awards Forfeited	-126,781
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments Other than Options, Nonvested, Number	411,580
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$24.40
Equity Instruments Other Than Options, Vested in Period	0
Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$24.29
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$24.40
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Awards Granted	417,784
Equity Awards Forfeited	-6,204
Minimum [Member] | Performance Shares [Member]
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Potential Vesting Percentage Range of Shares	0.00%
Maximum [Member] | Performance Shares [Member]
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Potential Vesting Percentage Range of Shares	200.00%
Class B Common Unit [Member]
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Equity-based Compensation Plan Modification, Incremental Compensation Cost			$6,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$119	$125.65
Equity-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Weighted-Average Volatility		65.50%	65.26%
Weighted-Average Risk-Free Rate		0.18%	0.19%
Dividend Yield		0.00%	0.00%
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Awards Outstanding, Beginning of Year		216,483
Equity Awards Granted		400
Equity Awards Forfeited		-860
Equity Awards Repurchased/Settled		-216,023
Equity Awards Outstanding, End of Period		0	216,483
Equity Awards Vested		0
2013 Long Term Incentive Plan [Member]
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Number of Units Authorized	11,700,000
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	7,541,891
2013 Long Term Incentive Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options, Grants in Period, Gross	1,245,513
MPK Plan Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value				$1,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				10 years 0 months 0 days
Equity-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Equity Awards Outstanding, Beginning of Year		66,137
Equity Awards Granted		0
Equity Awards Forfeited		-2,228
Equity Awards Repurchased/Settled		63,909
Equity Awards Outstanding, End of Period		0
Equity Awards Vested		0

Earnings_per_Share_Details

Earnings per Share (Details)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Weighted Average Number of Shares Outstanding, Basic	170.6	156.6	145.1
Effect of diluted securities	2.2	2.1	0.7
Weighted Average Number of Shares Outstanding, Diluted	172.8	158.7	145.8
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0	0

Deferred_Compensation_Plan_Det

Deferred Compensation Plan (Details) (USD $)

12 Months Ended

3 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Mar. 31, 2016

Aug. 01, 2013

9-May-14

Mar. 31, 2014

Feb. 21, 2014

Jan. 22, 2014

Oct. 18, 2013

Mar. 08, 2013

Mar. 10, 2010

Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]

deferred compensation arrangement with individual, units authorized for issuance

28,500

Deferred Compensation Arrangement with Individual, Units Outstanding

28,500

Redemption premium added to debt face amount, RDU plan

$0.10

$1.40

RDU plan cash retention pool

15

Charge for payment of RDU Plan cash retention pool

0

[1]

7.5

[1]

Deferred Compensation Arrangement with Individual, Requisite Service Period

3 years 0 months 0 days

RDU Plan, Compensation Expense

8.8

16.8

8.4

RDU Plan, Liability

30.4

21.8

Subordinated Debt [Member]

Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]

Debt Instrument, Repurchased Face Amount

324

42.5

50

20

30

155

50

28.5

2015 [Member]

Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]

RDU Plan, unrecognized compensation expense

5

2016 through 2017 [Member]

Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]

RDU Plan, unrecognized compensation expense

3

Scenario, Forecast [Member]

Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]

Second RDU Cash Retention Payment

$7.50

[1]

See Note 12 for additional discussion of this transaction.

Profit_Sharing_And_401K_Plan_D

Profit Sharing And 401(K) Plan (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Profit sharing plan expense	$21.90	$17.30	$14.60

Equity_Investments_Details

Equity Investments (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Investments [Abstract]
Equity Method Investment, Ownership Percentage	35.00%
Equity Method Investment, Percentage Available to be Acquired	65.00%
Payments to Acquire Equity Method Investments	$86.80	$0	$0
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$119.20

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 01, 2014	Aug. 05, 2014	Mar. 20, 2014
Related Party Transaction [Line Items]
Management Fee	$0	$2.50	$5
Net proceeds used for termination of Management Services Agreement		24.4
Senior notes due 2019 [Member]
Related Party Transaction [Line Items]
Debt Instrument, Repurchased Face Amount				$541.40	$234.70	$25

Segment_Information_Segment_Re

Segment Information Segment Reporting (Details) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
IPO and Secondary-offering related expenses														$75,000,000
Revenue, Net	3,050,100,000	3,266,100,000	3,106,000,000	2,652,300,000	2,713,300,000		2,864,300,000		2,779,300,000		2,411,700,000		12,074,500,000	10,768,600,000		10,128,200,000
Income (loss) from operations	164,300,000	184,700,000	188,200,000	135,800,000	142,000,000	[1]	92,900,000	[1]	153,600,000	[1]	120,100,000	[1]	673,000,000	508,600,000	[2]	510,600,000
Depreciation and amortization expense													-207,900,000	-208,200,000		-210,200,000
Segment Reporting Information, Additional Information [Abstract]
Number of Reportable Segments													2
Number of operating segments which do not meet reporting unit quantitative threshold													3
Net sales to the federal government, Percentage													7.00%	7.00%		10.00%
Net sales to customers outside of the US, Percent													4.00%	4.00%		4.00%
Long-Lived Assets in Foreign Countries, Percent	1.00%				1.00%								1.00%	1.00%
Equity Method Investment, Ownership Percentage	35.00%												35.00%
Public Segment: Government Agencies, Education and Healthcare [Member]
Segment Reporting Information [Line Items]
Revenue, Net													4,879,400,000	4,164,500,000		4,023,000,000
Income (loss) from operations													313,200,000	246,500,000	[2]	246,700,000
Depreciation and amortization expense													-43,800,000	-44,000,000		-44,000,000
Corporate [Member]
Segment Reporting Information [Line Items]
Revenue, Net	1,691,000,000	1,622,700,000	1,656,200,000	1,505,600,000	1,553,000,000		1,465,800,000		1,537,400,000		1,403,900,000
Segment Reporting Information, Additional Information [Abstract]
IPO- and secondary-offering related expenses														26,400,000
Public [Member]
Segment Reporting Information [Line Items]
Revenue, Net	1,169,100,000	1,468,800,000	1,271,600,000	969,900,000	990,500,000		1,244,600,000		1,082,600,000		846,800,000
Segment Reporting Information, Additional Information [Abstract]
IPO- and secondary-offering related expenses														14,400,000
Other [Member]
Segment Reporting Information [Line Items]
Revenue, Net	190,000,000	174,600,000	178,200,000	176,800,000	169,800,000		153,900,000		159,300,000		161,000,000		719,600,000	644,000,000		592,400,000
Income (loss) from operations													32,900,000	27,200,000	[2]	18,600,000
Depreciation and amortization expense													-8,800,000	-8,600,000		-9,300,000
Segment Reporting Information, Additional Information [Abstract]
IPO- and secondary-offering related expenses														3,600,000
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue, Net													0	0		0
Income (loss) from operations													-112,900,000	-128,400,000	[2]	-103,700,000
Depreciation and amortization expense													-59,000,000	-58,300,000		-59,300,000
Segment Reporting Information, Additional Information [Abstract]
IPO- and secondary-offering related expenses														30,600,000
Corporate Segment: Private Sector Business [Member]
Segment Reporting Information [Line Items]
Revenue, Net													6,475,500,000	5,960,100,000		5,512,800,000
Income (loss) from operations													439,800,000	363,300,000	[2]	349,000,000
Depreciation and amortization expense													-96,300,000	-97,300,000		-97,600,000
Federal [Member] | Public [Member]
Segment Reporting Information [Line Items]
Revenue, Net													$884,200,000	$764,400,000		$964,700,000
[1]	(3)The third quarter of 2013 included pre-tax IPO-related charges of $74.1 million. See Note 9 for additional discussion of the IPO.
[2]	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.

Segment_Information_Segment_Re1

Segment Information Segment Reporting, by Products and Services (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Net Sales from External Customer [Line Items]
Net sales to customers outside of the US, Percent									4.00%		4.00%		4.00%
Revenue, Net	$3,050,100,000	$3,266,100,000	$3,106,000,000	$2,652,300,000	$2,713,300,000	$2,864,300,000	$2,779,300,000	$2,411,700,000	$12,074,500,000		$10,768,600,000		$10,128,200,000
Revenue net, by Product and Service, Percentage									100.00%		100.00%		100.00%
Long-Lived Assets in Foreign Countries, Percent	1.00%				1.00%				1.00%		1.00%
Notebooks/Mobile Devices [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									2,352,300,000		1,698,400,000		1,462,800,000
Revenue net, by Product and Service, Percentage									19.50%		15.80%		14.40%
NetComm Products [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									1,615,900,000		1,486,300,000		1,351,500,000
Revenue net, by Product and Service, Percentage									13.40%		13.80%		13.30%
Enterprise and Data Storage (Including Drives) [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									1,024,300,000		999,200,000		981,500,000
Revenue net, by Product and Service, Percentage									8.50%		9.30%		9.70%
Other Hardware [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									4,549,200,000		4,178,500,000		4,075,700,000
Revenue net, by Product and Service, Percentage									37.60%		38.80%		40.30%
Software [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									2,076,700,000		1,993,100,000		1,877,700,000
Revenue net, by Product and Service, Percentage									17.20%		18.50%		18.50%
Services [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									371,400,000		332,700,000		285,000,000
Revenue net, by Product and Service, Percentage									3.10%		3.10%		2.80%
Other [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									84,700,000	[1]	80,400,000	[1]	94,000,000	[1]
Revenue net, by Product and Service, Percentage									0.70%	[1]	0.70%	[1]	1.00%	[1]
Public [Member]
Net Sales from External Customer [Line Items]
Revenue, Net	1,169,100,000	1,468,800,000	1,271,600,000	969,900,000	990,500,000	1,244,600,000	1,082,600,000	846,800,000
Federal [Member] | Public [Member]
Net Sales from External Customer [Line Items]
Revenue, Net									$884,200,000		$764,400,000		$964,700,000
[1]	Includes items such as delivery charges to customers and certain commission revenue.

Supplemental_Guarantor_Informa2

Supplemental Guarantor Information Condensed Consolidating Balance Sheets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	$344.50	$188.10	$37.90	$99.90
Accounts receivable, net of allowance for doubtful accounts	1,561.10	1,451
Merchandise inventory	337.5	382
Miscellaneous receivables	155.6	146.3
Prepaid expenses and other	54.7	46.1
Total current assets	2,453.40	2,213.50
Property and equipment, net	137.2	131.1
Equity Method Investments	86.7	0
Goodwill	2,217.60	2,220.30	2,209.30
Other intangible assets, net	1,168.80	1,328
Deferred financing costs, net	33	30.1	53.2
Other assets	3.2	1.6
Total assets	6,099.90	5,924.60
Accounts payable-trade	704	662.8
Accounts payable-inventory financing	332.1	256.6
Current maturities of long-term debt	15.4	45.4
Deferred revenue	81.3	94.8
Total current liabilities	1,468	1,402.60
Debt	3,174.60	3,205.80
Deferred income taxes	475	563.5
Other liabilities	45.8	41
Total long-term liabilities	3,695.40	3,810.30
Total shareholders' (deficit) equity	936.5	711.7	136.5	-7.3
Total liabilities and shareholders' (deficit) equity	6,099.90	5,924.60
Parent Guarantor [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	0	0	0	0
Accounts receivable, net of allowance for doubtful accounts	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
Equity Method Investments	0
Goodwill	0	0
Other intangible assets, net	0	0
Deferred financing costs, net	0	0
Other assets	4.3	4.9
Investments in and advances to subsidiaries	932.2	706.8
Total assets	936.5	711.7
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
Debt	0	0
Deferred income taxes	0	0
Other liabilities	0	0
Total long-term liabilities	0	0
Total shareholders' (deficit) equity	936.5	711.7
Total liabilities and shareholders' (deficit) equity	936.5	711.7
Subsidiary Issuer [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	346.4	196.5	48	102.1
Accounts receivable, net of allowance for doubtful accounts	0	0
Merchandise inventory	0	0
Miscellaneous receivables	56.1	49.9
Prepaid expenses and other	11	10.7
Total current assets	413.5	257.1
Property and equipment, net	80.5	69.7
Equity Method Investments	86.7
Goodwill	751.8	751.9
Other intangible assets, net	320	338.5
Deferred financing costs, net	33	30.1
Other assets	3.2	1.4
Investments in and advances to subsidiaries	2,784.50	2,909.40
Total assets	4,473.20	4,358.10
Accounts payable-trade	23.9	21.4
Accounts payable-inventory financing	0	0
Current maturities of long-term debt	15.4	45.4
Deferred revenue	0	0
Accrued expenses	137.8	163.5
Total current liabilities	177.1	230.3
Debt	3,174.60	3,205.80
Deferred income taxes	146.7	178.3
Other liabilities	42.6	36.9
Total long-term liabilities	3,363.90	3,421
Total shareholders' (deficit) equity	932.2	706.8
Total liabilities and shareholders' (deficit) equity	4,473.20	4,358.10
Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	0	0	0	15.8
Accounts receivable, net of allowance for doubtful accounts	1,479.10	1,375.90
Merchandise inventory	333.9	378.9
Miscellaneous receivables	93.3	91
Prepaid expenses and other	46	33.4
Total current assets	1,952.30	1,879.20
Property and equipment, net	55.5	59.6
Equity Method Investments	0
Goodwill	1,439	1,439
Other intangible assets, net	843.6	982.8
Deferred financing costs, net	0	0
Other assets	0.4	0.1
Investments in and advances to subsidiaries	0	0
Total assets	4,290.80	4,360.70
Accounts payable-trade	671.9	637.3
Accounts payable-inventory financing	332.1	256.6
Current maturities of long-term debt	0	0
Deferred revenue	79.9	89.9
Accrued expenses	193.6	175.1
Total current liabilities	1,277.50	1,158.90
Debt	0	0
Deferred income taxes	331.3	388.4
Other liabilities	3.7	3.6
Total long-term liabilities	335	392
Total shareholders' (deficit) equity	2,678.30	2,809.80
Total liabilities and shareholders' (deficit) equity	4,290.80	4,360.70
Non-Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	24.6	14	9.8	8.1
Accounts receivable, net of allowance for doubtful accounts	82	75.1
Merchandise inventory	3.6	3.1
Miscellaneous receivables	6.2	5.4
Prepaid expenses and other	1.5	5.1
Total current assets	117.9	102.7
Property and equipment, net	1.2	1.8
Equity Method Investments	0
Goodwill	26.8	29.4
Other intangible assets, net	5.2	6.7
Deferred financing costs, net	0	0
Other assets	1.4	0.9
Investments in and advances to subsidiaries	0	0
Total assets	152.5	141.5
Accounts payable-trade	34.7	26.5
Accounts payable-inventory financing	0	0
Current maturities of long-term debt	0	0
Deferred revenue	1.4	4.9
Accrued expenses	7.9	7.5
Total current liabilities	44	38.9
Debt	0	0
Deferred income taxes	1.3	1.6
Other liabilities	1	1.4
Total long-term liabilities	2.3	3
Total shareholders' (deficit) equity	106.2	99.6
Total liabilities and shareholders' (deficit) equity	152.5	141.5
Co-Issuer [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	0	0	0	0
Accounts receivable, net of allowance for doubtful accounts	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
Equity Method Investments	0
Goodwill	0	0
Other intangible assets, net	0	0
Deferred financing costs, net	0	0
Other assets	0	0
Investments in and advances to subsidiaries	0	0
Total assets	0	0
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
Debt	0	0
Deferred income taxes	0	0
Other liabilities	0	0
Total long-term liabilities	0	0
Total shareholders' (deficit) equity	0	0
Total liabilities and shareholders' (deficit) equity	0	0
Consolidating Adjustments [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	-26.5	-22.4	-19.9	-26.1
Accounts receivable, net of allowance for doubtful accounts	0	0
Merchandise inventory	0	0
Miscellaneous receivables	0	0
Prepaid expenses and other	-3.8	-3.1
Total current assets	-30.3	-25.5
Property and equipment, net		0
Equity Method Investments	0
Goodwill	0	0
Other intangible assets, net	0	0
Deferred financing costs, net	0	0
Other assets	-6.1	-5.7
Investments in and advances to subsidiaries	-3,716.70	-3,616.20
Total assets	-3,753.10	-3,647.40
Accounts payable-trade	-26.5	-22.4
Accounts payable-inventory financing	0	0
Current maturities of long-term debt	0	0
Deferred revenue	0	0
Accrued expenses	-4.1	-3.1
Total current liabilities	-30.6	-25.5
Debt	0	0
Deferred income taxes	-4.3	-4.8
Other liabilities	-1.5	-0.9
Total long-term liabilities	-5.8	-5.7
Total shareholders' (deficit) equity	-3,716.70	-3,616.20
Total liabilities and shareholders' (deficit) equity	-3,753.10	-3,647.40
Consolidated [Member]
Supplemental Guarantor Information [Line Items]
Cash and cash equivalents	344.5	188.1	37.9	99.9
Accounts receivable, net of allowance for doubtful accounts	1,561.10	1,451
Merchandise inventory	337.5	382
Miscellaneous receivables	155.6	146.3
Prepaid expenses and other	54.7	46.1
Total current assets	2,453.40	2,213.50
Property and equipment, net	137.2	131.1
Equity Method Investments	86.7
Goodwill	2,217.60	2,220.30
Other intangible assets, net	1,168.80	1,328
Deferred financing costs, net	33	30.1
Other assets	3.2	1.6
Investments in and advances to subsidiaries	0	0
Total assets	6,099.90	5,924.60
Accounts payable-trade	704	662.8
Accounts payable-inventory financing	332.1	256.6
Current maturities of long-term debt	15.4	45.4
Deferred revenue	81.3	94.8
Accrued expenses	335.2	343
Total current liabilities	1,468	1,402.60
Debt	3,174.60	3,205.80
Deferred income taxes	475	563.5
Other liabilities	45.8	41
Total long-term liabilities	3,695.40	3,810.30
Total shareholders' (deficit) equity	936.5	711.7
Total liabilities and shareholders' (deficit) equity	$6,099.90	$5,924.60

Supplemental_Guarantor_Informa3

Supplemental Guarantor Information Consolidating Statements of Operations (Details) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Supplemental Guarantor Information [Line Items]
Long-term Debt, Gross	$3,192,400,000												$3,192,400,000
Revenue, Net	3,050,100,000	3,266,100,000	3,106,000,000	2,652,300,000	2,713,300,000		2,864,300,000		2,779,300,000		2,411,700,000		12,074,500,000	10,768,600,000		10,128,200,000
Cost of sales													10,153,200,000	9,008,300,000		8,458,600,000
Gross Profit	491,900,000	507,300,000	496,900,000	425,200,000	448,300,000		458,400,000		451,600,000		402,000,000		1,921,300,000	1,760,300,000		1,669,600,000
Selling and administrative expenses													1,110,300,000	1,120,900,000		1,029,500,000
Advertising expense													138,000,000	130,800,000		129,500,000
Income (loss) from operations	164,300,000	184,700,000	188,200,000	135,800,000	142,000,000	[1]	92,900,000	[1]	153,600,000	[1]	120,100,000	[1]	673,000,000	508,600,000	[2]	510,600,000
Interest Income (Expense), Net													197,300,000	250,100,000		307,400,000
Net (loss) gain on extinguishments of long-term debt													-90,700,000	-64,000,000		-17,200,000
Other income, net													2,700,000	1,000,000		100,000
Income (loss) before income taxes													387,700,000	195,500,000		186,100,000
Income tax benefit (expense)													-142,800,000	-62,700,000		-67,100,000
Net income (loss)	51,800,000	55,600,000	86,600,000	50,900,000	60,000,000	[1]	-2,200,000	[1]	46,700,000	[1]	28,300,000	[1]	244,900,000	132,800,000		119,000,000
Parent Guarantor [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													0	0		0
Cost of sales													0	0		0
Gross Profit													0	0		0
Selling and administrative expenses													0	24,400,000		0
Advertising expense													0	0		0
Income (loss) from operations													0	-24,400,000		0
Interest Income (Expense), Net													0	0		0
Net (loss) gain on extinguishments of long-term debt													0	0		0
Management fee													0	0		0
Other income, net													0	0		0
Income (loss) before income taxes													0	-24,400,000		0
Income tax benefit (expense)													0	9,200,000		0
Equity in earnings (loss) of subsidiaries													244,900,000	148,000,000		119,000,000
(Loss) income before equity in earnings (loss) of subsidiaries													0	-15,200,000		0
Net income (loss)													244,900,000	132,800,000		119,000,000
Subsidiary Issuer [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													0	0		0
Cost of sales													0	0		0
Gross Profit													0	0		0
Selling and administrative expenses													112,800,000	103,900,000		103,700,000
Advertising expense													0	0		0
Income (loss) from operations													-112,800,000	-103,900,000		-103,700,000
Interest Income (Expense), Net													-197,700,000	-250,600,000		-308,000,000
Net (loss) gain on extinguishments of long-term debt													-90,700,000	-64,000,000		-17,200,000
Management fee													3,900,000	4,300,000		3,800,000
Other income, net													1,200,000	-500,000		0
Income (loss) before income taxes													-396,100,000	-414,700,000		-425,100,000
Income tax benefit (expense)													141,000,000	142,200,000		210,600,000
Equity in earnings (loss) of subsidiaries													500,000,000	420,500,000		333,500,000
(Loss) income before equity in earnings (loss) of subsidiaries													-255,100,000	-272,500,000		-214,500,000
Net income (loss)													244,900,000	148,000,000		119,000,000
Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													11,542,300,000	10,293,300,000		9,683,000,000
Cost of sales													9,684,900,000	8,592,100,000		8,071,500,000
Gross Profit													1,857,400,000	1,701,200,000		1,611,500,000
Selling and administrative expenses													962,300,000	957,300,000		891,600,000
Advertising expense													134,000,000	126,800,000		125,100,000
Income (loss) from operations													761,100,000	617,100,000		594,800,000
Interest Income (Expense), Net													100,000	200,000		400,000
Net (loss) gain on extinguishments of long-term debt													0	0		0
Management fee													0	0		0
Other income, net													1,500,000	1,200,000		200,000
Income (loss) before income taxes													762,700,000	618,500,000		595,400,000
Income tax benefit (expense)													-278,100,000	-209,500,000		-272,600,000
Equity in earnings (loss) of subsidiaries													0	0		0
(Loss) income before equity in earnings (loss) of subsidiaries													484,600,000	409,000,000		322,800,000
Net income (loss)													484,600,000	409,000,000		322,800,000
Non-Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													532,200,000	475,300,000		445,200,000
Cost of sales													468,300,000	416,200,000		387,100,000
Gross Profit													63,900,000	59,100,000		58,100,000
Selling and administrative expenses													35,200,000	35,300,000		34,200,000
Advertising expense													4,000,000	4,000,000		4,400,000
Income (loss) from operations													24,700,000	19,800,000		19,500,000
Interest Income (Expense), Net													300,000	300,000		200,000
Net (loss) gain on extinguishments of long-term debt													0	0		0
Management fee													-3,900,000	-4,300,000		-3,800,000
Other income, net													0	300,000		-100,000
Income (loss) before income taxes													21,100,000	16,100,000		15,800,000
Income tax benefit (expense)													-5,700,000	-4,600,000		-5,100,000
Equity in earnings (loss) of subsidiaries													0	0		0
(Loss) income before equity in earnings (loss) of subsidiaries													15,400,000	11,500,000		10,700,000
Net income (loss)													15,400,000	11,500,000		10,700,000
Co-Issuer [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													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 (loss) from operations													0	0		0
Interest Income (Expense), Net													0	0		0
Net (loss) gain on extinguishments of long-term debt													0	0		0
Management fee													0	0		0
Other income, net													0	0		0
Income (loss) before income taxes													0	0		0
Income tax benefit (expense)													0	0		0
Equity in earnings (loss) of subsidiaries													0	0		0
(Loss) income before equity in earnings (loss) of subsidiaries													0	0		0
Net income (loss)													0	0		0
Consolidating Adjustments [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													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 (loss) from operations													0	0		0
Interest Income (Expense), Net													0	0		0
Net (loss) gain on extinguishments of long-term debt													0	0		0
Management fee													0	0		0
Other income, net													0	0		0
Income (loss) before income taxes													0	0		0
Income tax benefit (expense)													0	0		0
Equity in earnings (loss) of subsidiaries													-744,900,000	-568,500,000		-452,500,000
(Loss) income before equity in earnings (loss) of subsidiaries													0	0		0
Net income (loss)													-744,900,000	-568,500,000		-452,500,000
Consolidated [Member]
Supplemental Guarantor Information [Line Items]
Revenue, Net													12,074,500,000	10,768,600,000		10,128,200,000
Cost of sales													10,153,200,000	9,008,300,000		8,458,600,000
Gross Profit													1,921,300,000	1,760,300,000		1,669,600,000
Selling and administrative expenses													1,110,300,000	1,120,900,000		1,029,500,000
Advertising expense													138,000,000	130,800,000		129,500,000
Income (loss) from operations													673,000,000	508,600,000		510,600,000
Interest Income (Expense), Net													-197,300,000	-250,100,000		-307,400,000
Net (loss) gain on extinguishments of long-term debt													-90,700,000	-64,000,000		-17,200,000
Management fee													0	0		0
Other income, net													2,700,000	1,000,000		100,000
Income (loss) before income taxes													387,700,000	195,500,000		186,100,000
Income tax benefit (expense)													-142,800,000	-62,700,000		-67,100,000
Equity in earnings (loss) of subsidiaries													0	0		0
(Loss) income before equity in earnings (loss) of subsidiaries													244,900,000	132,800,000		119,000,000
Net income (loss)													$244,900,000	$132,800,000		$119,000,000
[1]	(3)The third quarter of 2013 included pre-tax IPO-related charges of $74.1 million. See Note 9 for additional discussion of the IPO.
[2]	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.

Supplemental_Guarantor_Informa4

Supplemental Guarantor Information Condensed Consolidated Statements of Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$234.60	$126.10	$121.50
Parent Guarantor [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	234.6	126.1	121.5
Subsidiary Issuer [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	234.6	141.3	121.5
Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	484.6	409	322.8
Non-Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	5.1	4.8	13.2
Co-Issuer [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	0	0	0
Consolidating Adjustments [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	-724.3	-555.1	-457.5
Consolidated [Member]
Supplemental Guarantor Information [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$234.60	$126.10	$121.50

Supplemental_Guarantor_Informa5

Supplemental Guarantor Information Condensed Consolidating Statements of Cash Flows (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	$435	$366.30	$317.40
Capital expenditures	-55	-47.1	-41.4
Payments to Acquire Equity Method Investments	-86.8	0	0
Premium payments on interest rate cap agreements	-2.1	0	-0.3
Net cash used in investing activities	-164.8	-47.1	-41.7
Proceeds from borrowings under revolving credit facility	0	63	289
Repayments of borrowings under revolving credit facility	0	-63	-289
Repayments of long-term debt	-15.4	-51.1	-201
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Payments to extinguish long-term debt	-1,299	-2,047.40	-243.2
Payments of debt financing costs	-21.9	-6.1	-2.1
Net change in accounts payable-inventory financing	75.5	7.4	-29.5
Payment of incentive compensation plan withholding taxes	0	-24.1	0
Proceeds from Stock Options Exercised	1.3	0	0
Net proceeds from issuance of common shares	0	424.7	0
Proceeds from Coworker Stock Purchase Plan	5.8	0	0
Dividends paid	-33.6	-7.3	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0.3	0.6	0
Net cash provided by (used in) financing activities	-112	-168.3	-338
Effect of exchange rate changes on cash and cash equivalents	-1.8	-0.7	0.3
Net increase (decrease) in cash and cash equivalents	156.4	150.2	-62
Cash and cash equivalents - beginning of period	188.1	37.9	99.9
Cash and cash equivalents - end of period	344.5	188.1	37.9
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	-20.9	0	0
Parent Guarantor [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	0	-15.2	0
Capital expenditures	0	0	0
Payments to Acquire Equity Method Investments	0
Premium payments on interest rate cap agreements			0
Net cash used in investing activities	0	0	0
Proceeds from borrowings under revolving credit facility		0	0
Repayments of borrowings under revolving credit facility		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
Payments of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Payment of incentive compensation plan withholding taxes		0
Proceeds from Stock Options Exercised	0
Net proceeds from issuance of common shares		424.7
Proceeds from Coworker Stock Purchase Plan	0
Dividends paid	-33.6	-7.3
Excess Tax Benefit from Share-based Compensation, Financing Activities	0
Advances to (from) affiliates	33.6	-402.2	0
Other financing activities		0	0
Net cash provided by (used in) financing activities	0	15.2	0
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) 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
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	0
Payments for Derivative Instrument, Financing Activities	0
Subsidiary Issuer [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	-120.4	-130.3	-204.3
Capital expenditures	-47.9	-40.8	-27
Payments to Acquire Equity Method Investments	-86.8
Premium payments on interest rate cap agreements			-0.3
Net cash used in investing activities	-157.7	-40.8	-27.3
Proceeds from borrowings under revolving credit facility		63	289
Repayments of borrowings under revolving credit facility		-63	-289
Repayments of long-term debt	-15.4	-51.1	-201
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Payments to extinguish long-term debt	-1,299	-2,047.40	-243.2
Payments of debt financing costs	-21.9	-6.1	-2.1
Net change in accounts payable-inventory financing	0	0	0
Payment of incentive compensation plan withholding taxes		-4
Proceeds from Stock Options Exercised	1.3
Net proceeds from issuance of common shares		0
Proceeds from Coworker Stock Purchase Plan	5.8
Dividends paid	0	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0.3
Advances to (from) affiliates	581.9	892.6	486
Other financing activities		0.4	2.1
Net cash provided by (used in) financing activities	428	319.6	177.5
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	149.9	148.5	-54.1
Cash and cash equivalents - beginning of period	196.5	48	102.1
Cash and cash equivalents - end of period	346.4	196.5	48
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	-20.9
Payments for Derivative Instrument, Financing Activities	2.1
Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	547.7	508.8	514.2
Capital expenditures	-7.1	-6.2	-14
Payments to Acquire Equity Method Investments	0
Premium payments on interest rate cap agreements			0
Net cash used in investing activities	-7.1	-6.2	-14
Proceeds from borrowings under revolving credit facility		0	0
Repayments of borrowings under revolving credit facility		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
Payments of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	75.5	7.4	-29.5
Payment of incentive compensation plan withholding taxes		-19.6
Proceeds from Stock Options Exercised	0
Net proceeds from issuance of common shares		0
Proceeds from Coworker Stock Purchase Plan	0
Dividends paid	0	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0
Advances to (from) affiliates	-616.1	-490.4	-486.5
Other financing activities		0	0
Net cash provided by (used in) financing activities	-540.6	-502.6	-516
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	0	0	-15.8
Cash and cash equivalents - beginning of period	0	0	15.8
Cash and cash equivalents - end of period	0	0	0
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	0
Payments for Derivative Instrument, Financing Activities	0
Non-Guarantor Subsidiaries [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	11.8	5.5	1.3
Capital expenditures	0	-0.1	-0.4
Payments to Acquire Equity Method Investments	0
Premium payments on interest rate cap agreements			0
Net cash used in investing activities	0	-0.1	-0.4
Proceeds from borrowings under revolving credit facility		0	0
Repayments of borrowings under revolving credit facility		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
Payments of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Payment of incentive compensation plan withholding taxes		-0.5
Proceeds from Stock Options Exercised	0
Net proceeds from issuance of common shares		0
Proceeds from Coworker Stock Purchase Plan	0
Dividends paid	0	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0
Advances to (from) affiliates	0.6	0	0.5
Other financing activities		0	0
Net cash provided by (used in) financing activities	0.6	-0.5	0.5
Effect of exchange rate changes on cash and cash equivalents	-1.8	-0.7	0.3
Net increase (decrease) in cash and cash equivalents	10.6	4.2	1.7
Cash and cash equivalents - beginning of period	14	9.8	8.1
Cash and cash equivalents - end of period	24.6	14	9.8
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	0
Payments for Derivative Instrument, Financing Activities	0
Co-Issuer [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	0	0	0
Capital expenditures	0	0	0
Payments to Acquire Equity Method Investments	0
Premium payments on interest rate cap agreements			0
Net cash used in investing activities	0	0	0
Proceeds from borrowings under revolving credit facility		0	0
Repayments of borrowings under revolving credit facility		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
Payments of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Payment of incentive compensation plan withholding taxes		0
Proceeds from Stock Options Exercised	0
Net proceeds from issuance of common shares		0
Proceeds from Coworker Stock Purchase Plan	0
Dividends paid	0	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0
Advances to (from) affiliates	0	0	0
Other financing activities		0	0
Net cash provided by (used in) financing activities	0	0	0
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) 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
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	0
Payments for Derivative Instrument, Financing Activities	0
Consolidating Adjustments [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	-4.1	-2.5	6.2
Capital expenditures	0	0	0
Payments to Acquire Equity Method Investments	0
Premium payments on interest rate cap agreements			0
Net cash used in investing activities	0	0	0
Proceeds from borrowings under revolving credit facility		0	0
Repayments of borrowings under revolving credit facility		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
Payments of debt financing costs	0	0	0
Net change in accounts payable-inventory financing	0	0	0
Payment of incentive compensation plan withholding taxes		0
Proceeds from Stock Options Exercised	0
Net proceeds from issuance of common shares		0
Proceeds from Coworker Stock Purchase Plan	0
Dividends paid	0	0
Advances to (from) affiliates	0	0	0
Other financing activities		0	0
Net cash provided by (used in) financing activities	0	0	0
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net increase (decrease) in cash and cash equivalents	-4.1	-2.5	6.2
Cash and cash equivalents - beginning of period	-22.4	-19.9	-26.1
Cash and cash equivalents - end of period	-26.5	-22.4	-19.9
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	0
Payments for Derivative Instrument, Financing Activities	0
Consolidated [Member]
Supplemental Guarantor Information [Line Items]
Net cash provided by (used in) operating activities	435	366.3	317.4
Capital expenditures	-55	-47.1	-41.4
Payments to Acquire Equity Method Investments	-86.8
Premium payments on interest rate cap agreements	-2.1		-0.3
Net cash used in investing activities	-164.8	-47.1	-41.7
Proceeds from borrowings under revolving credit facility		63	289
Repayments of borrowings under revolving credit facility		-63	-289
Repayments of long-term debt	-15.4	-51.1	-201
Proceeds from issuance of long-term debt	1,175	1,535.20	135.7
Payments to extinguish long-term debt	-1,299	-2,047.40	-243.2
Payments of debt financing costs	-21.9	-6.1	-2.1
Net change in accounts payable-inventory financing	75.5	7.4	-29.5
Payment of incentive compensation plan withholding taxes		-24.1
Proceeds from Stock Options Exercised	1.3
Net proceeds from issuance of common shares	5.8	424.7
Dividends paid	-33.6	-7.3
Excess Tax Benefit from Share-based Compensation, Financing Activities	0.3
Advances to (from) affiliates	0	0	0
Other financing activities		0.4	2.1
Net cash provided by (used in) financing activities	-112	-168.3	-338
Effect of exchange rate changes on cash and cash equivalents	-1.8	-0.7	0.3
Net increase (decrease) in cash and cash equivalents	156.4	150.2	-62
Cash and cash equivalents - beginning of period	188.1	37.9	99.9
Cash and cash equivalents - end of period	344.5	188.1	37.9
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	($20.90)

Supplemental_Guarantor_Informa6

Supplemental Guarantor Information Additional Details (Details) (USD $)

Dec. 31, 2014

9-May-14

Mar. 31, 2014

Feb. 21, 2014

Jan. 22, 2014

Dec. 31, 2013

Oct. 18, 2013

Aug. 01, 2013

Mar. 08, 2013

Mar. 10, 2010

Aug. 05, 2014

Jul. 02, 2013

Dec. 01, 2014

Mar. 20, 2014

In Millions, unless otherwise specified

Debt Instrument [Line Items]

Long-term Debt, Gross

$3,192.40

Subordinated Debt [Member]

Debt Instrument [Line Items]

Debt Instrument, Repurchased Face Amount

42.5

50

20

30

155

324

50

28.5

Long-term Debt, Gross

0

92.5

Senior Notes due 2022 [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

600

Senior secured notes due 2018 [Member]

Debt Instrument [Line Items]

Debt Instrument, Repurchased Face Amount

325

175

Long-term Debt, Gross

0

325

Senior notes due 2019 [Member]

Debt Instrument [Line Items]

Debt Instrument, Repurchased Face Amount

234.7

541.4

25

Long-term Debt, Gross

503.9

1,305

Senior Notes due 2024 [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

$575

Selected_Quarterly_Financial_R1

Selected Quarterly Financial Results (Details) (USD $)	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
IPO Related Expenses									$74,100,000
Revenue, Net	3,050,100,000		3,266,100,000		3,106,000,000		2,652,300,000		2,713,300,000		2,864,300,000		2,779,300,000		2,411,700,000		12,074,500,000	10,768,600,000		10,128,200,000
Gross Profit	491,900,000		507,300,000		496,900,000		425,200,000		448,300,000		458,400,000		451,600,000		402,000,000		1,921,300,000	1,760,300,000		1,669,600,000
Income (loss) from operations	164,300,000		184,700,000		188,200,000		135,800,000		142,000,000	[1]	92,900,000	[1]	153,600,000	[1]	120,100,000	[1]	673,000,000	508,600,000	[2]	510,600,000
Net income (loss)	51,800,000		55,600,000		86,600,000		50,900,000		60,000,000	[1]	-2,200,000	[1]	46,700,000	[1]	28,300,000	[1]	244,900,000	132,800,000		119,000,000
Basic	$0.30	[3]	$0.33	[3]	$0.51	[3]	$0.30	[3]	$0.35	[1],[3]	($0.01)	[1],[3]	$0.32	[1],[3]	$0.19	[1],[3]	$1.44	$0.85		$0.82
Diluted	$0.30	[3]	$0.32	[3]	$0.50	[3]	$0.30	[3]	$0.35	[1],[3]	($0.01)	[1],[3]	$0.32	[1],[3]	$0.19	[1],[3]	$1.42	$0.84		$0.82
Corporate [Member]
Revenue, Net	1,691,000,000		1,622,700,000		1,656,200,000		1,505,600,000		1,553,000,000		1,465,800,000		1,537,400,000		1,403,900,000
Corporate [Member] | Medium/Large [Member]
Revenue, Net	1,440,300,000		1,374,800,000		1,395,400,000		1,274,800,000		1,322,300,000	[4]	1,241,300,000	[4]	1,308,500,000	[4]	1,180,500,000	[4]
Corporate [Member] | Small Business [Member]
Revenue, Net	250,700,000		247,900,000		260,800,000		230,800,000		230,700,000	[4]	224,500,000	[4]	228,900,000	[4]	223,400,000	[4]
Public [Member]
Revenue, Net	1,169,100,000		1,468,800,000		1,271,600,000		969,900,000		990,500,000		1,244,600,000		1,082,600,000		846,800,000
Public [Member] | Government [Member]
Revenue, Net	440,800,000		441,300,000		313,100,000		254,200,000		327,300,000		375,300,000		295,700,000		252,300,000
Public [Member] | Education [Member]
Revenue, Net	342,600,000		632,800,000		527,000,000		321,600,000		282,800,000		513,400,000		420,600,000		232,200,000
Public [Member] | Healthcare [Member]
Revenue, Net	385,700,000		394,700,000		431,500,000		394,100,000		380,400,000		355,900,000		366,300,000		362,300,000
Other [Member]
Revenue, Net	190,000,000		174,600,000		178,200,000		176,800,000		169,800,000		153,900,000		159,300,000		161,000,000		719,600,000	644,000,000		592,400,000
Income (loss) from operations																	$32,900,000	$27,200,000	[2]	$18,600,000
[1]	(3)The third quarter of 2013 included pre-tax IPO-related charges of $74.1 million. See Note 9 for additional discussion of the IPO.
[2]	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.
[3]	(1) Basic and diluted net income (loss) 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 (loss) per share.
[4]	(2)Net sales for the corporate channels (medium/large and small business) have been restated for all periods presented above to conform with the new corporate hierarchy presented for first quarter of 2014.

Subsequent_Events_Subsequent_E

Subsequent Events Subsequent Events (Details) (USD $)	12 Months Ended			3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Declared	$0.20	$0.04	$0
Payments for Derivative Instrument, Investing Activities	$2.10	$0	$0.30
Subsequent Event [Member]
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Declared				$0.07
Cap agreement effective January 14, 2015-2017 [Member]
Subsequent Event [Line Items]
Number of Interest Rate Derivatives Held	14
Derivative, Notional Amount	1,000
Payments for Derivative Instrument, Investing Activities	2.1
Cap agreement effective January 14, 2015-2017 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of Interest Rate Derivatives Held				6
Derivative, Notional Amount				400
Payments for Derivative Instrument, Investing Activities				$0.50
Derivative, Cap Interest Rate				2.00%

Valuation_And_Qualifying_Accou1

Valuation And Qualifying Accounts (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$5.40	$5.40	$5.40
Charged to Costs and Expenses	5.4	2.8	3.9
Deductions	-5.1	-2.8	-3.9
Balance at End of Period	5.7	5.4	5.4
Reserve for Sales Returns [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	5.1	4.4	4.5
Charged to Costs and Expenses	36.2	35	33.2
Deductions	-36.2	-34.3	-33.3
Balance at End of Period	$5.10	$5.10	$4.40