v2.4.1.9

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 us-gaap_StockRepurchaseProgramAuthorizedAmount1 |
Stock Repurchased During Period, Shares |  | 0 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other IPO Related Expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,400,000 cdw_OtherIPORelatedExpenses | [1] |  |  |  |
Employee Stock Purchase Plan, discount to market price, percent |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.00%cdw_EmployeeStockPurchasePlandiscounttomarketpricepercent |  |  |  |  |  |  |
Equity-based compensation expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,400,000 us-gaap_AllocatedShareBasedCompensationExpense |  | 46,600,000 us-gaap_AllocatedShareBasedCompensationExpense |  | 22,100,000 us-gaap_AllocatedShareBasedCompensationExpense |  |  |
Proceeds from shares sold by certain selling stockholders |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 cdw_Proceedsfromsharessoldbycertainsellingstockholders |  |  |  |  |  |  |
Preferred Stock, Shares Issued |  |  | 0 us-gaap_PreferredStockSharesIssued |  |  |  |  |  |  |  | 0 us-gaap_PreferredStockSharesIssued |  |  |  | 0 us-gaap_PreferredStockSharesIssued |  | 0 us-gaap_PreferredStockSharesIssued |  |  |  |  |
Secondary-offering related expenses |  |  | 200,000 cdw_Secondaryofferingrelatedexpenses |  | 300,000 cdw_Secondaryofferingrelatedexpenses |  | 500,000 cdw_Secondaryofferingrelatedexpenses |  | 400,000 cdw_Secondaryofferingrelatedexpenses |  |  |  |  |  | 1,400,000 cdw_Secondaryofferingrelatedexpenses | [1] | 600,000 cdw_Secondaryofferingrelatedexpenses |  |  |  |  |
Proceeds from Issuance Initial Public Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 424,700,000 us-gaap_ProceedsFromIssuanceInitialPublicOffering |  |  |  |  |
Stockholders' Equity Note, Stock Split, Conversion Ratio | 143.0299613 us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Par Value |  |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  |  |  |  |  |  |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  |  |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  |  |  |  |
Preferred Stock, Shares Authorized |  |  | 100,000,000 us-gaap_PreferredStockSharesAuthorized |  |  |  |  |  |  |  | 100,000,000 us-gaap_PreferredStockSharesAuthorized |  |  |  | 100,000,000 us-gaap_PreferredStockSharesAuthorized |  | 100,000,000 us-gaap_PreferredStockSharesAuthorized |  |  |  |  |
Preferred Stock, Par or Stated Value Per Share |  |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |  |  |  |  |  |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |  |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |  |  |  |
Preferred Stock, Shares Outstanding |  |  | 0 us-gaap_PreferredStockSharesOutstanding |  |  |  |  |  |  |  | 0 us-gaap_PreferredStockSharesOutstanding |  |  |  | 0 us-gaap_PreferredStockSharesOutstanding |  | 0 us-gaap_PreferredStockSharesOutstanding |  |  |  |  |
Common Stock, Shares Authorized |  |  | 1,000,000,000 us-gaap_CommonStockSharesAuthorized |  |  |  |  |  |  |  | 1,000,000,000 us-gaap_CommonStockSharesAuthorized |  |  |  | 1,000,000,000 us-gaap_CommonStockSharesAuthorized |  | 1,000,000,000 us-gaap_CommonStockSharesAuthorized |  |  |  |  |
Common Stock, Dividends, Per Share, Cash Paid |  |  | $ 0.0675 us-gaap_CommonStockDividendsPerShareCashPaid |  | $ 0.0425 us-gaap_CommonStockDividendsPerShareCashPaid |  | $ 0.0425 us-gaap_CommonStockDividendsPerShareCashPaid |  | $ 0.0425 us-gaap_CommonStockDividendsPerShareCashPaid |  | $ 0.0425 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.0000 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.0000 us-gaap_CommonStockDividendsPerShareCashPaid | $ 0.0000 us-gaap_CommonStockDividendsPerShareCashPaid |  |  |  |  |  |  |  |
Dividends, Common Stock, Cash |  |  | 11,700,000 us-gaap_DividendsCommonStockCash |  | 7,300,000 us-gaap_DividendsCommonStockCash |  | 7,300,000 us-gaap_DividendsCommonStockCash |  | 7,300,000 us-gaap_DividendsCommonStockCash |  | 7,300,000 us-gaap_DividendsCommonStockCash | 0 us-gaap_DividendsCommonStockCash | 0 us-gaap_DividendsCommonStockCash | 0 us-gaap_DividendsCommonStockCash |  |  |  |  |  |  |  |
Coworker Stock Purchase Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity-based compensation expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.0 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_StatementEquityComponentsAxis = cdw_CoworkerStockPurchasePlanMember |  |  |  |  |  |  |
IPO [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23,250,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_IPOMember |  |
Share Price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 17.00 us-gaap_SharePrice / us-gaap_StatementEquityComponentsAxis = us-gaap_IPOMember
IPO Over-allotment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,487,500 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = cdw_IPOOverallotmentMember |  |  |  |  |
Secondary Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold by certain selling stockholders |  |  | 15,000,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryOfferingMember |  | 15,000,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryOfferingMember |  | 15,000,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryOfferingMember |  | 10,000,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryOfferingMember |  |  |  |  |  |  |  | 15,000,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryOfferingMember |  |  |  |  |
Secondary offering over-allotment [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares sold by certain selling stockholders |  |  | 2,250,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryofferingoverallotmentMember | [2] | 0 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryofferingoverallotmentMember | [2],[3] | 2,250,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryofferingoverallotmentMember | [2] | 1,500,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryofferingoverallotmentMember | [2] |  |  |  |  |  |  | 2,250,000 cdw_Sharessoldbycertainsellingstockholders / us-gaap_StatementEquityComponentsAxis = cdw_SecondaryofferingoverallotmentMember | [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

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