v2.4.1.9

Segment Information Segment Reporting (Details) (USD $)

3 Months Ended

12 Months Ended

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Segment Reporting Information [Line Items]

IPO and Secondary-offering related expenses

$ 75,000,000cdw_IPOandSecondaryofferingrelatedexpenses

Revenue, Net

3,050,100,000us-gaap_SalesRevenueNet

3,266,100,000us-gaap_SalesRevenueNet

3,106,000,000us-gaap_SalesRevenueNet

2,652,300,000us-gaap_SalesRevenueNet

2,713,300,000us-gaap_SalesRevenueNet

2,864,300,000us-gaap_SalesRevenueNet

2,779,300,000us-gaap_SalesRevenueNet

2,411,700,000us-gaap_SalesRevenueNet

12,074,500,000us-gaap_SalesRevenueNet

10,768,600,000us-gaap_SalesRevenueNet

10,128,200,000us-gaap_SalesRevenueNet

Income (loss) from operations

164,300,000us-gaap_OperatingIncomeLoss

184,700,000us-gaap_OperatingIncomeLoss

188,200,000us-gaap_OperatingIncomeLoss

135,800,000us-gaap_OperatingIncomeLoss

142,000,000us-gaap_OperatingIncomeLoss

^[1]

92,900,000us-gaap_OperatingIncomeLoss

^[1]

153,600,000us-gaap_OperatingIncomeLoss

^[1]

120,100,000us-gaap_OperatingIncomeLoss

^[1]

673,000,000us-gaap_OperatingIncomeLoss

508,600,000us-gaap_OperatingIncomeLoss

^[2]

510,600,000us-gaap_OperatingIncomeLoss

Depreciation and amortization expense

(207,900,000)us-gaap_DepreciationDepletionAndAmortization

(208,200,000)us-gaap_DepreciationDepletionAndAmortization

(210,200,000)us-gaap_DepreciationDepletionAndAmortization

Segment Reporting Information, Additional Information [Abstract]

Number of Reportable Segments

2us-gaap_NumberOfReportableSegments

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

3cdw_NumberOfOperatingSegmentsWhichDoNotMeetReportableUnitQuantitativeThreshold

Net sales to the federal government, Percentage

7.00%us-gaap_ConcentrationRiskPercentage1

7.00%us-gaap_ConcentrationRiskPercentage1

10.00%us-gaap_ConcentrationRiskPercentage1

Net sales to customers outside of the US, Percent

4.00%cdw_NetSalesToCustomersOutsideOfUsPercent

4.00%cdw_NetSalesToCustomersOutsideOfUsPercent

4.00%cdw_NetSalesToCustomersOutsideOfUsPercent

Long-Lived Assets in Foreign Countries, Percent

1.00%cdw_LongLivedAssetsInForeignCountriesPercent

1.00%cdw_LongLivedAssetsInForeignCountriesPercent

1.00%cdw_LongLivedAssetsInForeignCountriesPercent

1.00%cdw_LongLivedAssetsInForeignCountriesPercent

Equity Method Investment, Ownership Percentage

35.00%us-gaap_EquityMethodInvestmentOwnershipPercentage

35.00%us-gaap_EquityMethodInvestmentOwnershipPercentage

Public Segment: Government Agencies, Education and Healthcare [Member]

Segment Reporting Information [Line Items]

Revenue, Net

4,879,400,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

4,164,500,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

4,023,000,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

Income (loss) from operations

313,200,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

246,500,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

^[2]

246,700,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

Depreciation and amortization expense

(43,800,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

(44,000,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

(44,000,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicSegmentGovernmentAgenciesEducationandHealthcareMember

Corporate [Member]

Segment Reporting Information [Line Items]

Revenue, Net

1,691,000,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,622,700,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,656,200,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,505,600,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,553,000,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,465,800,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,537,400,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

1,403,900,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

Segment Reporting Information, Additional Information [Abstract]

IPO- and secondary-offering related expenses

26,400,000cdw_IPOandsecondaryofferingrelatedexpenses
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentMember

Public [Member]

Segment Reporting Information [Line Items]

Revenue, Net

1,169,100,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

1,468,800,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

1,271,600,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

969,900,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

990,500,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

1,244,600,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

1,082,600,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

846,800,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

Segment Reporting Information, Additional Information [Abstract]

IPO- and secondary-offering related expenses

14,400,000cdw_IPOandsecondaryofferingrelatedexpenses
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

Other [Member]

Segment Reporting Information [Line Items]

Revenue, Net

190,000,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

174,600,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

178,200,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

176,800,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

169,800,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

153,900,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

159,300,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

161,000,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

719,600,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

644,000,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

592,400,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

Income (loss) from operations

32,900,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

27,200,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

^[2]

18,600,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

Depreciation and amortization expense

(8,800,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

(8,600,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

(9,300,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

Segment Reporting Information, Additional Information [Abstract]

IPO- and secondary-offering related expenses

3,600,000cdw_IPOandsecondaryofferingrelatedexpenses
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember

Corporate, Non-Segment [Member]

Segment Reporting Information [Line Items]

Revenue, Net

0us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

0us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

0us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

Income (loss) from operations

(112,900,000)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

(128,400,000)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

^[2]

(103,700,000)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

Depreciation and amortization expense

(59,000,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

(58,300,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

(59,300,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

Segment Reporting Information, Additional Information [Abstract]

IPO- and secondary-offering related expenses

30,600,000cdw_IPOandsecondaryofferingrelatedexpenses
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_CorporateNonSegmentMember

Corporate Segment: Private Sector Business [Member]

Segment Reporting Information [Line Items]

Revenue, Net

6,475,500,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

5,960,100,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

5,512,800,000us-gaap_SalesRevenueNet
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

Income (loss) from operations

439,800,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

363,300,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

^[2]

349,000,000us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

Depreciation and amortization expense

(96,300,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

(97,300,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

(97,600,000)us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_CorporateSegmentPrivateSectorBusinessMember

Federal [Member] | Public [Member]

Segment Reporting Information [Line Items]

Revenue, Net

$ 884,200,000us-gaap_SalesRevenueNet
/ cdw_PublicAxis
= cdw_FederalMember
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

$ 764,400,000us-gaap_SalesRevenueNet
/ cdw_PublicAxis
= cdw_FederalMember
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

$ 964,700,000us-gaap_SalesRevenueNet
/ cdw_PublicAxis
= cdw_FederalMember
/ us-gaap_StatementBusinessSegmentsAxis
= cdw_PublicMember

[1]	(3)The third quarter of 2013 included pre-tax IPO-related charges of $74.1 million. See Note 9 for additional discussion of the IPO.
[2]	(1) Includes $75.0 million of IPO- and secondary-offering related expenses, as follows: Corporate $26.4 million; Public $14.4 million; Other $3.6 million; and Headquarters $30.6 million.

X

- Definition

IPO- and secondary-offering related expenses

+ References

No definition available.

+ Details

Name:	cdw_IPOandsecondaryofferingrelatedexpenses
Namespace Prefix:	cdw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

IPO and Secondary-offering related expenses

+ References

No definition available.

+ Details

Name:	cdw_IPOandSecondaryofferingrelatedexpenses
Namespace Prefix:	cdw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of long-lived assets located in foreign countries in total, in which the entity holds assets, as a percentage of total long-lived assets.

+ References

No definition available.

+ Details

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

X

- Definition

Net sales to external customers attributed to all foreign countries, in total, in which the company generates revenue, as a percent of total revenues.

+ References

No definition available.

+ Details

Name:	cdw_NetSalesToCustomersOutsideOfUsPercent
Namespace Prefix:	cdw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

Name:	us-gaap_DepreciationDepletionAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_SalesRevenueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

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

X

- Details

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

X

- Details

Name:	cdw_PublicAxis=cdw_FederalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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

X

- Details

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