Debt - Narrative (Details) $ in Millions	Mar. 31, 2022 USD ($)
Senior unsecured revolving loan facility
Debt Instrument [Line Items]
Additional borrowing capacity	$ 1,000
Undrawn letters of credit	1
Senior unsecured revolving loan facility \| Accounts Payable, Inventory Financing
Debt Instrument [Line Items]
Amount owed under Revolving loan financing agreement	437
Senior unsecured term loan facility
Debt Instrument [Line Items]
Debt Instrument, Annual Principal Payment	36
2023 and thereafter	$ 18

Amount owed under Revolving loan financing agreement

No definition available.

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

- Definition

Long Term Debt Maturities Repayments Of Principal Year Two And Thereafter

+ References

No definition available.

+ Details

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

- Definition

Amount of the total principal payments made during the annual reporting period.

+ References

Reference 1: 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 http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Details

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

- Details

Name:	cdw_InventoryFinancingAgreementsAxis=cdw_AccountsPayableInventoryFinancingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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