v2.4.1.9

Equity Investments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Investments [Abstract]
Equity Method Investment, Ownership Percentage	35.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
Equity Method Investment, Percentage Available to be Acquired	65.00%cdw_EquityMethodInvestmentPercentageAvailabletobeAcquired
Payments to Acquire Equity Method Investments	$ 86.8us-gaap_PaymentsToAcquireEquityMethodInvestments	$ 0us-gaap_PaymentsToAcquireEquityMethodInvestments	$ 0us-gaap_PaymentsToAcquireEquityMethodInvestments
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 119.2us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity

X

- Details

Name:	cdw_EquityInvestmentsAbstract
Namespace Prefix:	cdw_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Equity Method Investment, Percentage Available to be Acquired

+ References

No definition available.

+ Details

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

X

- Definition

Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

+ 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)(3)

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

+ Details

Name:	us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585

+ Details

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