v2.4.1.9

Deferred Compensation Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended					3 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Mar. 31, 2016	Aug. 01, 2013	May 09, 2014	Mar. 31, 2014	Feb. 21, 2014	Jan. 22, 2014	Oct. 18, 2013	Mar. 08, 2013	Mar. 10, 2010
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
deferred compensation arrangement with individual, units authorized for issuance	28,500cdw_Deferredcompensationarrangementwithindividualunitsauthorizedforissuance
Deferred Compensation Arrangement with Individual, Units Outstanding	28,500cdw_DeferredCompensationArrangementwithIndividualUnitsOutstanding
Redemption premium added to debt face amount, RDU plan	$ 0.1cdw_RedemptionpremiumaddedtodebtfaceamountRDUplan		$ 1.4cdw_RedemptionpremiumaddedtodebtfaceamountRDUplan
RDU plan cash retention pool							15.0cdw_RDUplancashretentionpool
Charge for payment of RDU Plan cash retention pool	0cdw_ChargeforpaymentofRDUPlancashretentionpool	[1]	7.5cdw_ChargeforpaymentofRDUPlancashretentionpool	[1]
Deferred Compensation Arrangement with Individual, Requisite Service Period	3 years 0 months 0 days
RDU Plan, Compensation Expense	8.8us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense		16.8us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense		8.4us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
RDU Plan, Liability	30.4us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability		21.8us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability
Subordinated Debt [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Debt Instrument, Repurchased Face Amount							324.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	42.5us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	50.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	20.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	30.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	155.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	50.0us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember	28.5us-gaap_DebtInstrumentRepurchasedFaceAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SubordinatedDebtMember
2015 [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
RDU Plan, unrecognized compensation expense	5cdw_DeferredCompensationArrangementWithIndividualUnrecognizedCompensationExpense / cdw_PeriodofRecognitionAxis = cdw_A2015MemberDomain
2016 through 2017 [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
RDU Plan, unrecognized compensation expense	3cdw_DeferredCompensationArrangementWithIndividualUnrecognizedCompensationExpense / cdw_PeriodofRecognitionAxis = cdw_A2016through2017MemberMember
Scenario, Forecast [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Second RDU Cash Retention Payment						$ 7.5cdw_SecondRDUCashRetentionPayment / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember
[1] See Note 12 for additional discussion of this transaction.

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- Definition

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- Definition

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- Definition

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- Definition

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- Definition

RDU plan cash retention pool

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- Definition

Redemption premium added to debt face amount, RDU plan

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- Definition

Second RDU Cash Retention Payment

+ References

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Balance Type:	debit
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- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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X

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 710

-SubTopic 10

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

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- Definition

The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 710

-SubTopic 10

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

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X

- Definition

Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 710

-SubTopic 10

-Section 55

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6409961&loc=d3e20487-108367



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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