Name:	cdw_LongtermDebtCurrentMaturitiesGross
Namespace Prefix:	cdw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying amount of long-term debt, net of unamortized deferred financing costs, discount, or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

No definition available.

Name:	cdw_LongtermDebtExcludingCurrentMaturitiesNetofDeferredFinancingCostsDiscountorPremium
Namespace Prefix:	cdw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

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

Weighted average interest rate of long-term debt outstanding calculated at point in time.

No definition available.

Name:	us-gaap_LongtermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorSecuredAssetBasedRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorSecuredTermLoanFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_UnsecuredSeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesdue2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesdueMay2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesdue2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesDue2029Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesDueDecember2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_SeniorNotesDue2031Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=cdw_ReceivableFinancingLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: