v2.4.1.9

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	3cdw_NumberOfOperatingSegmentsWhichDoNotMeetReportableUnitQuantitativeThreshold
Goodwill Impairment Test, Income Approach Weight		75.00%cdw_GoodwillImpairmentTestIncomeApproachWeight	75.00%cdw_GoodwillImpairmentTestIncomeApproachWeight	75.00%cdw_GoodwillImpairmentTestIncomeApproachWeight
Goodwill Impairment Test, Market Approach Weight		25.00%cdw_GoodwillImpairmentTestMarketApproachWeight	25.00%cdw_GoodwillImpairmentTestMarketApproachWeight	25.00%cdw_GoodwillImpairmentTestMarketApproachWeight
Years Forecasted in Goodwill Impairment Income Approach		6cdw_YearsForecastedInGoodwillImpairmentIncomeApproach	6cdw_YearsForecastedInGoodwillImpairmentIncomeApproach	6cdw_YearsForecastedInGoodwillImpairmentIncomeApproach
Long-Term Consolidated Annual Growth Rate		3.50%cdw_LongTermConsolidatedAnnualGrowthRate	3.50%cdw_LongTermConsolidatedAnnualGrowthRate	3.50%cdw_LongTermConsolidatedAnnualGrowthRate
Corporate Reporting Unit [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		169.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / cdw_ReportingUnitsAxis = cdw_CorporateReportingUnitMember	107.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / cdw_ReportingUnitsAxis = cdw_CorporateReportingUnitMember	49.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / cdw_ReportingUnitsAxis = cdw_CorporateReportingUnitMember
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.00%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / cdw_ReportingUnitsAxis = cdw_CorporateReportingUnitMember	10.00%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / cdw_ReportingUnitsAxis = cdw_CorporateReportingUnitMember	11.50%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / cdw_ReportingUnitsAxis = cdw_CorporateReportingUnitMember
Public Segment Reporting Unit [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		147.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / cdw_ReportingUnitsAxis = cdw_PublicReportingUnitMember	82.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / cdw_ReportingUnitsAxis = cdw_PublicReportingUnitMember	44.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / cdw_ReportingUnitsAxis = cdw_PublicReportingUnitMember
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.00%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / cdw_ReportingUnitsAxis = cdw_PublicReportingUnitMember	10.00%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / cdw_ReportingUnitsAxis = cdw_PublicReportingUnitMember	11.50%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / cdw_ReportingUnitsAxis = cdw_PublicReportingUnitMember
Canada Operating Segment [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		276.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / us-gaap_StatementBusinessSegmentsAxis = cdw_CanadaOperatingSegmentMember	167.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / us-gaap_StatementBusinessSegmentsAxis = cdw_CanadaOperatingSegmentMember	104.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / us-gaap_StatementBusinessSegmentsAxis = cdw_CanadaOperatingSegmentMember
Goodwill, Assumptions Used in Impairment Test, Discount Rate		9.30%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / us-gaap_StatementBusinessSegmentsAxis = cdw_CanadaOperatingSegmentMember	10.30%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / us-gaap_StatementBusinessSegmentsAxis = cdw_CanadaOperatingSegmentMember	11.80%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / us-gaap_StatementBusinessSegmentsAxis = cdw_CanadaOperatingSegmentMember
CDW Advanced Services Operating Segment [Member]
Goodwill [Line Items]
Reporting unit fair value in excess of carrying value		78.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / us-gaap_StatementBusinessSegmentsAxis = cdw_CDWAdvancedServicesOperatingSegmentMember	168.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / us-gaap_StatementBusinessSegmentsAxis = cdw_CDWAdvancedServicesOperatingSegmentMember	17.00%cdw_ReportingUnitFairValueInExcessOfCarryingValue / us-gaap_StatementBusinessSegmentsAxis = cdw_CDWAdvancedServicesOperatingSegmentMember
Goodwill, Assumptions Used in Impairment Test, Discount Rate		11.50%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / us-gaap_StatementBusinessSegmentsAxis = cdw_CDWAdvancedServicesOperatingSegmentMember	10.50%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / us-gaap_StatementBusinessSegmentsAxis = cdw_CDWAdvancedServicesOperatingSegmentMember	12.00%cdw_GoodwillAssumptionsUsedInImpairmentTestDiscountRate / us-gaap_StatementBusinessSegmentsAxis = cdw_CDWAdvancedServicesOperatingSegmentMember

X

- Definition

Discount rate used in the impairment test for Goodwill.

+ References

No definition available.

+ Details

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

X

- 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

X

- 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

X

- 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

X

- 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

X

- 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

X

- 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

X

- Details

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

X

- 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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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