Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended |
Mar. 31, 2019 | Mar. 31, 2018 |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 3,957.9 | $ 3,606.4 |
Revenue net, by Product and Service, Percentage | 100.00% | 100.00% |
Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 1,736.2 | $ 1,565.8 |
Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 355.6 | 327.6 |
Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,330.7 | 1,230 |
Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 535.4 | 483 |
Transferred at a point in time where CDW is principal | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 3,635.2 | 3,340.1 |
Transferred at a point in time where CDW is principal | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,581.8 | 1,426.3 |
Transferred at a point in time where CDW is principal | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 335.2 | 309.4 |
Transferred at a point in time where CDW is principal | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,243.3 | 1,171.4 |
Transferred at a point in time where CDW is principal | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 474.9 | 433 |
Transferred at a point in time where CDW is agent | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 183 | 165.4 |
Transferred at a point in time where CDW is agent | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 104 | 92.7 |
Transferred at a point in time where CDW is agent | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 19.8 | 16.5 |
Transferred at a point in time where CDW is agent | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 46.2 | 41.1 |
Transferred at a point in time where CDW is agent | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 13 | 15.1 |
Transferred over time where CDW is principal | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 139.7 | 100.9 |
Transferred over time where CDW is principal | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 50.4 | 46.8 |
Transferred over time where CDW is principal | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0.6 | 1.7 |
Transferred over time where CDW is principal | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 41.2 | 17.5 |
Transferred over time where CDW is principal | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 47.5 | 34.9 |
Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,736.2 | 1,565.8 |
Corporate | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,736.2 | 1,565.8 |
Corporate | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Corporate | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Corporate | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 355.6 | 327.6 |
Small Business | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Small Business | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 355.6 | 327.6 |
Small Business | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Small Business | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Government | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 488.4 | 418.5 |
Government | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Government | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Government | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 488.4 | 418.5 |
Government | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Education | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 400.4 | 397.2 |
Education | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Education | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Education | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 400.4 | 397.2 |
Education | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Healthcare | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 441.9 | 414.3 |
Healthcare | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Healthcare | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Healthcare | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 441.9 | 414.3 |
Healthcare | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 535.4 | 483 |
Other | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Other | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Other | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Other | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 535.4 | 483 |
Notebooks/Mobile Devices | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 977.1 | $ 865.9 |
Revenue net, by Product and Service, Percentage | 24.70% | 24.00% |
Netcomm Products | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 512.3 | $ 487.3 |
Revenue net, by Product and Service, Percentage | 12.90% | 13.50% |
Desktops | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 303.7 | $ 310.8 |
Revenue net, by Product and Service, Percentage | 7.70% | 8.60% |
Video | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 271.8 | $ 260.8 |
Revenue net, by Product and Service, Percentage | 6.90% | 7.20% |
Enterprise and Data Storage (Including Drives) | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 290.6 | $ 250.1 |
Revenue net, by Product and Service, Percentage | 7.30% | 7.00% |
Other Hardware | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 782.4 | $ 736.6 |
Revenue net, by Product and Service, Percentage | 19.80% | 20.40% |
Hardware | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 3,137.9 | $ 2,911.5 |
Revenue net, by Product and Service, Percentage | 79.30% | 80.70% |
Hardware | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 1,383.9 | $ 1,250.3 |
Hardware | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 295 | 273.1 |
Hardware | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,063.1 | 1,007 |
Hardware | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 395.9 | 381.1 |
Software | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 593.9 | $ 504 |
Revenue net, by Product and Service, Percentage | 15.00% | 14.00% |
Software | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 247.4 | $ 219.6 |
Software | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 48.3 | 42.8 |
Software | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 221 | 184.3 |
Software | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 77.2 | 57.3 |
Services | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 196.6 | $ 162.9 |
Revenue net, by Product and Service, Percentage | 5.00% | 4.50% |
Services | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 88.1 | $ 79.3 |
Services | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 7 | 6.3 |
Services | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 42.3 | 34.6 |
Services | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 59.2 | 42.7 |
Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 29.5 | $ 28 |
Revenue net, by Product and Service, Percentage | 0.70% | 0.80% |
Other | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 16.8 | $ 16.6 |
Other | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 5.3 | 5.4 |
Other | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 4.3 | 4.1 |
Other | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 3.1 | 1.9 |
United States | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 3,427.6 | 3,131.2 |
United States | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,732.9 | 1,564.4 |
United States | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 355.6 | 327.6 |
United States | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 1,330.7 | 1,230 |
United States | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 8.4 | 9.2 |
Rest of World | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 530.3 | 475.2 |
Rest of World | Operating Segments | Corporate | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 3.3 | 1.4 |
Rest of World | Operating Segments | Small Business | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Rest of World | Operating Segments | Public | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | 0 | 0 |
Rest of World | Operating Segments | Other | | |
Disaggregation of Revenue [Line Items] | | |
Net sales | $ 527 | $ 473.8 |