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	$ 0.1950us-gaap_CommonStockDividendsPerShareDeclared	$ 0.0425us-gaap_CommonStockDividendsPerShareDeclared	$ 0.0000us-gaap_CommonStockDividendsPerShareDeclared
Payments for Derivative Instrument, Investing Activities	$ 2.1us-gaap_PaymentsForDerivativeInstrumentInvestingActivities	$ 0us-gaap_PaymentsForDerivativeInstrumentInvestingActivities	$ 0.3us-gaap_PaymentsForDerivativeInstrumentInvestingActivities
Subsequent Event [Member]
Subsequent Event [Line Items]
Common Stock, Dividends, Per Share, Declared				$ 0.0675us-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	14us-gaap_NumberOfInterestRateDerivativesHeld / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member
Derivative, Notional Amount	1,000.0invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member
Payments for Derivative Instrument, Investing Activities	2.1us-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				6us-gaap_NumberOfInterestRateDerivativesHeld / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Derivative, Notional Amount				400.0invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = cdw_CapagreementeffectiveJanuary1420152017Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Payments for Derivative Instrument, Investing Activities				$ 0.5us-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

X

- 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: