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