v2.4.1.9

Subsequent Events Subsequent Events (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 12 Months Ended | 3 Months Ended
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2015
Subsequent Event [Line Items] |  |  |  |
Common Stock, Dividends, Per Share, Declared | $ 0.1950 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0425 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0000 us-gaap_CommonStockDividendsPerShareDeclared |
Payments for Derivative Instrument, Investing Activities | $ 2.1 us-gaap_PaymentsForDerivativeInstrumentInvestingActivities | $ 0 us-gaap_PaymentsForDerivativeInstrumentInvestingActivities | $ 0.3 us-gaap_PaymentsForDerivativeInstrumentInvestingActivities |
Subsequent Event [Member] |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Common Stock, Dividends, Per Share, Declared |  |  |  | $ 0.0675 us-gaap_CommonStockDividendsPerShareDeclared / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Cap agreement effective January 14, 2015-2017 [Member] |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Number of Interest Rate Derivatives Held | 14 us-gaap_NumberOfInterestRateDerivativesHeld / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member |  |  |
Derivative, Notional Amount | 1,000.0 invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member |  |  |
Payments for Derivative Instrument, Investing Activities | 2.1 us-gaap_PaymentsForDerivativeInstrumentInvestingActivities / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member |  |  |
Cap agreement effective January 14, 2015-2017 [Member] | Subsequent Event [Member] |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Number of Interest Rate Derivatives Held |  |  |  | 6 us-gaap_NumberOfInterestRateDerivativesHeld / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Derivative, Notional Amount |  |  |  | 400.0 invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Payments for Derivative Instrument, Investing Activities |  |  |  | $ 0.5 us-gaap_PaymentsForDerivativeInstrumentInvestingActivities / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Derivative, Cap Interest Rate |  |  |  | 2.00%us-gaap_DerivativeCapInterestRate / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract. + References No definition available. + Details
Name: | us-gaap_DerivativeCapInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of interest rate derivative instruments held by the entity at the reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5579245-113959 + Details
Name: | us-gaap_NumberOfInterestRateDerivativesHeld
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The cash outflow for derivative instruments during the period, which are classified as investing activities, excluding those designated as hedging instruments. + References No definition available. + Details
Name: | us-gaap_PaymentsForDerivativeInstrumentInvestingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeByNatureAxis=cdw_CapagreementeffectiveJanuary1420152017Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |