Goodwill And Other Intangible Assets Goodwill and Intangible Assets, Test for Impairment (Details)	12 Months Ended
Dec. 31, 2014	Dec. 01, 2014	Dec. 01, 2013	Dec. 01, 2012
Goodwill [Line Items]
Number of Reportable Segments	2us-gaap_NumberOfReportableSegments
Number of operating segments which do not meet reporting unit quantitative threshold	3
Goodwill Impairment Test, Income Approach Weight		75.00%	75.00%	75.00%
Goodwill Impairment Test, Market Approach Weight		25.00%	25.00%	25.00%
Years Forecasted in Goodwill Impairment Income Approach		6	6	6
Long-Term Consolidated Annual Growth Rate		3.50%	3.50%	3.50%
Corporate Reporting Unit [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		169.00%	107.00%	49.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.00%	10.00%	11.50%
Public Segment Reporting Unit [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		147.00%	82.00%	44.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.00%	10.00%	11.50%
Canada Operating Segment [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		276.00%	167.00%	104.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.30%	10.30%	11.80%
CDW Advanced Services Operating Segment [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		78.00%	168.00%	17.00%
Goodwill, Assumptions Used in Impairment Test, Discount Rate		11.50%	10.50%	12.00%

Discount rate used in the impairment test for Goodwill.

No definition available.

Name:	cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weight provided to the Income Approach in determining the fair value of goodwill for a given reporting unit as part of the test for impairment.

+ References

No definition available.

+ Details

Name:	cdw_GoodwillImpairmentTestIncomeApproachWeight
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weight given the Market Approach in calculating the fair value of goodwill for a given reporting unit as part of the test for impairment.

+ References

No definition available.

+ Details

Name:	cdw_GoodwillImpairmentTestMarketApproachWeight
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Long-Term Consolidated Annual Growth Rate

+ References

No definition available.

+ Details

Name:	cdw_LongTermConsolidatedAnnualGrowthRate
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of operating segments which do not meet reportable unit quantitative threshold

+ References

No definition available.

+ Details

Name:	cdw_NumberOfOperatingSegmentsWhichDoNotMeetReportableUnitQuantitativeThreshold
Namespace Prefix:	cdw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value of the reporting unit in excess of carrying value, expessed as a percent.

+ References

No definition available.

+ Details

Name:	cdw_ReportingUnitFairValueInExcessOfCarryingValue
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Years Forecasted in Goodwill Impairment Income Approach

+ References

No definition available.

+ Details

Name:	cdw_YearsForecastedInGoodwillImpairmentIncomeApproach
Namespace Prefix:	cdw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_GoodwillLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	cdw_ReportingUnitsAxis=cdw_CorporateReportingUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=cdw_CanadaOperatingSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=cdw_CDWAdvancedServicesOperatingSegmentMember
Namespace Prefix:
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Period Type: