Supplemental Guarantor Information - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 154.0	$ 205.8
Accounts receivable, net	3,002.2	2,671.2
Merchandise inventory	611.2	454.3
Miscellaneous receivables	395.1	316.4
Prepaid expenses and other	171.6	149.1
Total current assets	4,334.1	3,796.8
Operating lease right-of-use assets	131.8
Property and equipment, net	363.1	156.1
Goodwill	2,553.0	2,462.8	$ 2,479.6
Other intangible assets, net	594.1	712.2
Other assets	23.3	39.8
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	7,999.4	7,167.7
Current liabilities:
Accounts payable-trade	1,835.0	1,577.1
Accounts payable-inventory financing	429.9	429.3
Current maturities of long-term debt	34.1	25.3
Contract liabilities	252.2	178.3
Accrued expenses and other current liabilities	940.2	593.1
Total current liabilities	3,491.4	2,803.1
Long-term liabilities:
Debt	3,283.2	3,183.3
Deferred income taxes	62.4	141.9
Operating lease liabilities	131.1
Other liabilities	71.0	64.2
Total long-term liabilities	3,547.7	3,389.4
Total stockholders' equity	960.3	975.2	$ 985.6	$ 1,047.9
Total Liabilities and Stockholders' Equity	7,999.4	7,167.7
Reportable Legal Entities \| Parent Guarantor
Current assets:
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	0.0	0.0
Operating lease right-of-use assets	0.0
Property and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Other assets	1.4	1.4
Investment in and advances to subsidiaries	958.9	973.8
Total Assets	960.3	975.2
Current liabilities:
Accounts payable-trade	0.0	0.0
Accounts payable-inventory financing	0.0	0.0
Current maturities of long-term debt	0.0	0.0
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	0.0	0.0
Total current liabilities	0.0	0.0
Long-term liabilities:
Debt	0.0	0.0
Deferred income taxes	0.0	0.0
Operating lease liabilities	0.0
Other liabilities	0.0	0.0
Total long-term liabilities	0.0	0.0
Total stockholders' equity	960.3	975.2
Total Liabilities and Stockholders' Equity	960.3	975.2
Reportable Legal Entities \| Subsidiary Issuer
Current assets:
Cash and cash equivalents	73.9	176.0
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	97.9	110.6
Prepaid expenses and other	22.1	17.1
Total current assets	193.9	303.7
Operating lease right-of-use assets	75.4
Property and equipment, net	73.3	82.3
Goodwill	751.8	751.8
Other intangible assets, net	242.9	252.5
Other assets	25.7	49.8
Investment in and advances to subsidiaries	3,342.9	3,028.9
Total Assets	4,705.9	4,469.0
Current liabilities:
Accounts payable-trade	46.5	39.2
Accounts payable-inventory financing	0.1	0.2
Current maturities of long-term debt	14.9	14.9
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	291.3	217.6
Total current liabilities	352.8	271.9
Long-term liabilities:
Debt	3,229.5	3,121.3
Deferred income taxes	49.7	55.9
Operating lease liabilities	84.9
Other liabilities	30.1	46.1
Total long-term liabilities	3,394.2	3,223.3
Total stockholders' equity	958.9	973.8
Total Liabilities and Stockholders' Equity	4,705.9	4,469.0
Reportable Legal Entities \| Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	2,517.0	2,331.2
Merchandise inventory	524.9	387.4
Miscellaneous receivables	265.9	187.7
Prepaid expenses and other	99.9	93.8
Total current assets	3,407.7	3,000.1
Operating lease right-of-use assets	29.1
Property and equipment, net	259.0	52.0
Goodwill	1,454.3	1,437.8
Other intangible assets, net	177.6	300.0
Other assets	20.1	9.6
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	5,347.8	4,799.5
Current liabilities:
Accounts payable-trade	1,525.7	1,387.9
Accounts payable-inventory financing	378.9	406.1
Current maturities of long-term debt	12.4	4.0
Contract liabilities	146.4	95.6
Accrued expenses and other current liabilities	559.1	306.7
Total current liabilities	2,622.5	2,200.3
Long-term liabilities:
Debt	0.0	4.3
Deferred income taxes	0.0	60.5
Operating lease liabilities	22.9
Other liabilities	0.7	5.7
Total long-term liabilities	23.6	70.5
Total stockholders' equity	2,701.7	2,528.7
Total Liabilities and Stockholders' Equity	5,347.8	4,799.5
Reportable Legal Entities \| Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	98.9	46.7
Accounts receivable, net	485.2	340.0
Merchandise inventory	86.3	66.9
Miscellaneous receivables	31.3	18.1
Prepaid expenses and other	49.6	38.2
Total current assets	751.3	509.9
Operating lease right-of-use assets	27.3
Property and equipment, net	30.8	21.8
Goodwill	346.9	273.2
Other intangible assets, net	173.6	159.7
Other assets	171.9	140.2
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	1,501.8	1,104.8
Current liabilities:
Accounts payable-trade	281.6	166.9
Accounts payable-inventory financing	50.9	23.0
Current maturities of long-term debt	6.8	6.4
Contract liabilities	105.8	82.7
Accrued expenses and other current liabilities	89.8	68.8
Total current liabilities	534.9	347.8
Long-term liabilities:
Debt	53.7	57.7
Deferred income taxes	29.9	26.9
Operating lease liabilities	23.3
Other liabilities	218.8	172.2
Total long-term liabilities	325.7	256.8
Total stockholders' equity	641.2	500.2
Total Liabilities and Stockholders' Equity	1,501.8	1,104.8
Reportable Legal Entities \| Affiliated Entity
Current assets:
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	0.0	0.0
Operating lease right-of-use assets	0.0
Property and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Other assets	0.0	0.0
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	0.0	0.0
Current liabilities:
Accounts payable-trade	0.0	0.0
Accounts payable-inventory financing	0.0	0.0
Current maturities of long-term debt	0.0	0.0
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	0.0	0.0
Total current liabilities	0.0	0.0
Long-term liabilities:
Debt	0.0	0.0
Deferred income taxes	0.0	0.0
Operating lease liabilities	0.0
Other liabilities	0.0	0.0
Total long-term liabilities	0.0	0.0
Total stockholders' equity	0.0	0.0
Total Liabilities and Stockholders' Equity	0.0	0.0
Consolidating Adjustments
Current assets:
Cash and cash equivalents	(18.8)	(16.9)
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	(18.8)	(16.9)
Operating lease right-of-use assets	0.0
Property and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Other assets	(195.8)	(161.2)
Investment in and advances to subsidiaries	(4,301.8)	(4,002.7)
Total Assets	(4,516.4)	(4,180.8)
Current liabilities:
Accounts payable-trade	(18.8)	(16.9)
Accounts payable-inventory financing	0.0	0.0
Current maturities of long-term debt	0.0	0.0
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	0.0	0.0
Total current liabilities	(18.8)	(16.9)
Long-term liabilities:
Debt	0.0	0.0
Deferred income taxes	(17.2)	(1.4)
Operating lease liabilities	0.0
Other liabilities	(178.6)	(159.8)
Total long-term liabilities	(195.8)	(161.2)
Total stockholders' equity	(4,301.8)	(4,002.7)
Total Liabilities and Stockholders' Equity	$ (4,516.4)	$ (4,180.8)

Accounts payable inventory financing.

No definition available.

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

- Definition

Carrying value as of the balance sheet date of obligations incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).