Consolidated Statement Of Shareholders' (Deficit) Equity (USD $) In Millions, except Share data	Total	Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Preferred Stock [Member]	Common Stock [Member]
Balance at at Dec. 31, 2011	$ (7.3)us-gaap_StockholdersEquity	$ 2,184.7	$ (2,191.3)	$ (2.1)	$ 0	$ 1.4
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	2.8cdw_InvestmentFromParentCompany	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)	119.0us-gaap_NetIncomeLoss	0	119.0	0	0	0
Foreign currency translation adjustment	2.5	0	0	2.5	0	0
Balance at at Dec. 31, 2012	136.5us-gaap_StockholdersEquity	2,207.7	(2,073.0)	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)us-gaap_DividendsCommonStock	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)	132.8us-gaap_NetIncomeLoss	0	132.8	0	0	0
Foreign currency translation adjustment	(6.7)	0	0	(6.7)	0	0
Balance at at Dec. 31, 2013	711.7us-gaap_StockholdersEquity	2,688.1	(1,971.8)	(6.3)	0	1.7
Preferred Stock, Shares Issued at Dec. 31, 2013	0us-gaap_PreferredStockSharesIssued				0
Common Stock, Shares, Issued at Dec. 31, 2013	172,000,000us-gaap_CommonStockSharesIssued					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)us-gaap_DividendsCommonStock	0	(33.6)	0	0	0
Net income (loss)	244.9us-gaap_NetIncomeLoss	0	244.9	0	0	0
Foreign currency translation adjustment	(10.3)	0	0	(10.3)	0	0
Balance at at Dec. 31, 2014	$ 936.5us-gaap_StockholdersEquity	$ 2,711.9	$ (1,760.5)	$ (16.6)	$ 0	$ 1.7
Preferred Stock, Shares Issued at Dec. 31, 2014	0us-gaap_PreferredStockSharesIssued				0
Common Stock, Shares, Issued at Dec. 31, 2014	172,200,000us-gaap_CommonStockSharesIssued					172,200,000

Accrued charitable contribution related to the MPK Coworker Incentive Plan II, net of tax

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Incentive compensation plan units withheld for taxes

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Investment From Parent Company

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Reclassification to goodwill for accrued charitable contributions

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Stock Issued During Period, Shares, Accrued charitable contribution related to the MPK Coworker Incentive Plan II

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This element represents the amount of recognized equity-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized). Alternate captions include the words "stock-based compensation".

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This element represents the amount of recognized equity-based compensation related to stock options during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized).

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No definition available.

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Number of new stock issued during the period.

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Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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Value of stock issued as a result of the exercise of stock options.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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