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Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 5,146.4 | $ 4,365.7 | $ 9,983.9 | $ 8,754.9
Percentage of Total Net Sales | 100.00% | 100.00% | 100.00% | 100.00%
Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 1,983.3 | $ 1,557.5 | $ 3,788.9 | $ 3,468.5
Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 482.9 | 302.1 | 915.6 | 693.6
Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 2,080.7 | 2,022.1 | 4,002.4 | 3,547.4
Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 599.5 | 484.0 | 1,277.0 | 1,045.4
Transferred at a point in time where CDW is principal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 4,721.5 | 3,948.3 | 9,177.7 | 7,959.6
Transferred at a point in time where CDW is principal | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,789.2 | 1,387.2 | 3,416.9 | 3,128.2
Transferred at a point in time where CDW is principal | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 451.6 | 280.7 | 853.6 | 647.4
Transferred at a point in time where CDW is principal | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,953.5 | 1,854.2 | 3,779.4 | 3,258.8
Transferred at a point in time where CDW is principal | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 527.2 | 426.2 | 1,127.8 | 925.2
Transferred at a point in time where CDW is agent |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 251.4 | 214.2 | 472.1 | 409.3
Transferred at a point in time where CDW is agent | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 120.7 | 112.2 | 233.0 | 219.8
Transferred at a point in time where CDW is agent | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 25.9 | 18.9 | 52.8 | 40.9
Transferred at a point in time where CDW is agent | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 85.0 | 68.3 | 143.1 | 120.6
Transferred at a point in time where CDW is agent | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 19.8 | 14.8 | 43.2 | 28.0
Transferred over time where CDW is principal |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 173.5 | 203.2 | 334.1 | 386.0
Transferred over time where CDW is principal | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 73.4 | 58.1 | 139.0 | 120.5
Transferred over time where CDW is principal | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 5.4 | 2.5 | 9.2 | 5.3
Transferred over time where CDW is principal | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 42.2 | 99.6 | 79.9 | 168.0
Transferred over time where CDW is principal | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 52.5 | 43.0 | 106.0 | 92.2
Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,983.3 | 1,557.5 | 3,788.9 | 3,468.5
Corporate | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,983.3 | 1,557.5 | 3,788.9 | 3,468.5
Corporate | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Corporate | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Corporate | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 482.9 | 302.1 | 915.6 | 693.6
Small Business | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Small Business | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 482.9 | 302.1 | 915.6 | 693.6
Small Business | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Small Business | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Government |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 513.4 | 719.7 | 1,029.5 | 1,288.2
Government | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Government | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Government | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 513.4 | 719.7 | 1,029.5 | 1,288.2
Government | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Education |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,112.1 | 876.8 | 2,055.4 | 1,353.0
Education | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Education | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Education | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,112.1 | 876.8 | 2,055.4 | 1,353.0
Education | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Healthcare |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 455.2 | 425.6 | 917.5 | 906.2
Healthcare | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Healthcare | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Healthcare | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 455.2 | 425.6 | 917.5 | 906.2
Healthcare | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 599.5 | 484.0 | 1,277.0 | 1,045.4
Other | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Other | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Other | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Other | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 599.5 | 484.0 | 1,277.0 | 1,045.4
Hardware |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 4,225.6 | $ 3,549.2 | $ 8,195.2 | $ 7,018.6
Percentage of Total Net Sales | 82.10% | 81.30% | 82.10% | 80.20%
Hardware | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 1,586.5 | $ 1,211.6 | $ 3,007.3 | $ 2,729.5
Hardware | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 416.4 | 247.7 | 784.6 | 572.8
Hardware | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,763.9 | 1,724.8 | 3,431.8 | 2,940.0
Hardware | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 458.8 | 365.1 | 971.5 | 776.3
Notebooks/Mobile Devices |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 1,710.1 | $ 1,427.7 | $ 3,302.8 | $ 2,538.2
Percentage of Total Net Sales | 33.20% | 32.70% | 33.10% | 29.00%
Netcomm Products |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 483.8 | $ 471.2 | $ 938.4 | $ 926.0
Percentage of Total Net Sales | 9.40% | 10.80% | 9.40% | 10.60%
Desktops |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 293.7 | $ 254.4 | $ 558.9 | $ 636.7
Percentage of Total Net Sales | 5.70% | 5.80% | 5.60% | 7.30%
Video |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 410.5 | $ 246.8 | $ 736.5 | $ 560.3
Percentage of Total Net Sales | 8.00% | 5.70% | 7.40% | 6.40%
Enterprise and Data Storage (Including Drives) |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 242.5 | $ 200.1 | $ 502.1 | $ 440.9
Percentage of Total Net Sales | 4.70% | 4.60% | 5.00% | 5.00%
Other Hardware |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 1,085.0 | $ 949.0 | $ 2,156.5 | $ 1,916.5
Percentage of Total Net Sales | 21.10% | 21.70% | 21.60% | 21.90%
Software |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 637.8 | $ 572.3 | $ 1,243.3 | $ 1,225.7
Percentage of Total Net Sales | 12.40% | 13.10% | 12.50% | 14.00%
Software | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 267.6 | $ 238.9 | $ 534.6 | $ 511.1
Software | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 49.4 | 42.6 | 98.5 | 95.4
Software | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 242.5 | 222.5 | 433.9 | 457.6
Software | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 78.3 | 68.3 | 176.3 | 161.6
Services |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 251.7 | $ 214.8 | $ 485.6 | $ 445.4
Percentage of Total Net Sales | 4.90% | 4.90% | 4.90% | 5.10%
Services | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 110.9 | $ 93.1 | $ 213.5 | $ 193.1
Services | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 11.3 | 7.1 | 21.5 | 15.4
Services | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 70.1 | 66.2 | 128.0 | 134.1
Services | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 59.4 | 48.4 | 122.6 | 102.8
Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 31.3 | $ 29.4 | $ 59.8 | $ 65.2
Percentage of Total Net Sales | 0.60% | 0.70% | 0.50% | 0.70%
Other | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 18.3 | $ 13.9 | $ 33.5 | $ 34.8
Other | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 5.8 | 4.7 | 11.0 | 10.0
Other | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 4.2 | 8.6 | 8.7 | 15.7
Other | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 3.0 | 2.2 | 6.6 | 4.7
United States |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 4,544.5 | 3,870.9 | 8,707.0 | 7,701.7
United States | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 1,976.2 | 1,542.9 | 3,779.7 | 3,450.7
United States | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 482.9 | 302.1 | 915.6 | 693.6
United States | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 2,080.7 | 2,022.1 | 4,002.4 | 3,547.4
United States | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 4.7 | 3.8 | 9.3 | 10.0
Rest of World |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 601.9 | 494.8 | 1,276.9 | 1,053.2
Rest of World | Corporate |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 7.1 | 14.6 | 9.2 | 17.8
Rest of World | Small Business |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Rest of World | Public |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | 0.0 | 0.0 | 0.0 | 0.0
Rest of World | Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net sales | $ 594.8 | $ 480.2 | $ 1,267.7 | $ 1,035.4

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