Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Net sales	$ 6,215.5	$ 5,300.0	$ 18,310.4	$ 15,283.9
Percentage of Total Net Sales	100.00%	100.00%	100.00%	100.00%
Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 2,577.8	$ 2,067.3	$ 7,866.1	$ 5,856.2
Small Business
Disaggregation of Revenue [Line Items]
Net sales	491.2	467.1	1,515.2	1,382.7
Public
Disaggregation of Revenue [Line Items]
Net sales	2,424.3	2,153.9	6,700.3	6,156.3
Other
Disaggregation of Revenue [Line Items]
Net sales	722.2	611.7	2,228.8	1,888.7
Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	5,485.3	4,813.0	16,251.0	13,990.7
Transferred at a point in time where CDW is principal | Corporate
Disaggregation of Revenue [Line Items]
Net sales	2,216.3	1,851.0	6,833.4	5,267.9
Transferred at a point in time where CDW is principal | Small Business
Disaggregation of Revenue [Line Items]
Net sales	438.4	434.6	1,374.6	1,288.2
Transferred at a point in time where CDW is principal | Public
Disaggregation of Revenue [Line Items]
Net sales	2,189.4	1,984.8	6,062.1	5,764.2
Transferred at a point in time where CDW is principal | Other
Disaggregation of Revenue [Line Items]
Net sales	641.2	542.6	1,980.9	1,670.4
Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Net sales	382.3	288.8	1,051.5	760.9
Transferred at a point in time where CDW is agent | Corporate
Disaggregation of Revenue [Line Items]
Net sales	194.3	135.6	547.2	368.6
Transferred at a point in time where CDW is agent | Small Business
Disaggregation of Revenue [Line Items]
Net sales	36.3	27.8	104.0	80.6
Transferred at a point in time where CDW is agent | Public
Disaggregation of Revenue [Line Items]
Net sales	129.5	109.1	329.3	252.2
Transferred at a point in time where CDW is agent | Other
Disaggregation of Revenue [Line Items]
Net sales	22.2	16.3	71.0	59.5
Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Net sales	347.9	198.2	1,007.9	532.3
Transferred over time where CDW is principal | Corporate
Disaggregation of Revenue [Line Items]
Net sales	167.2	80.7	485.5	219.7
Transferred over time where CDW is principal | Small Business
Disaggregation of Revenue [Line Items]
Net sales	16.5	4.7	36.6	13.9
Transferred over time where CDW is principal | Public
Disaggregation of Revenue [Line Items]
Net sales	105.4	60.0	308.9	139.9
Transferred over time where CDW is principal | Other
Disaggregation of Revenue [Line Items]
Net sales	58.8	52.8	176.9	158.8
Corporate
Disaggregation of Revenue [Line Items]
Net sales	2,577.8	2,067.3	7,866.1	5,856.2
Corporate | Corporate
Disaggregation of Revenue [Line Items]
Net sales	2,577.8	2,067.3	7,866.1	5,856.2
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	491.2	467.1	1,515.2	1,382.7
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	491.2	467.1	1,515.2	1,382.7
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	788.4	568.8	1,941.8	1,598.3
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	788.4	568.8	1,941.8	1,598.3
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	1,021.1	1,103.6	2,965.2	3,159.0
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	1,021.1	1,103.6	2,965.2	3,159.0
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	614.8	481.5	1,793.3	1,399.0
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	614.8	481.5	1,793.3	1,399.0
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	722.2	611.7	2,228.8	1,888.7
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	722.2	611.7	2,228.8	1,888.7
Hardware
Disaggregation of Revenue [Line Items]
Net sales	$ 4,812.7	$ 4,263.7	$ 14,216.7	$ 12,460.3
Percentage of Total Net Sales	77.50%	80.50%	77.60%	81.40%
Hardware | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 1,958.1	$ 1,641.2	$ 5,931.0	$ 4,648.6
Hardware | Small Business
Disaggregation of Revenue [Line Items]
Net sales	399.5	400.7	1,262.7	1,185.3
Hardware | Public
Disaggregation of Revenue [Line Items]
Net sales	1,921.4	1,747.3	5,364.8	5,180.5
Hardware | Other
Disaggregation of Revenue [Line Items]
Net sales	533.7	474.5	1,658.2	1,445.9
Notebooks/Mobile Devices
Disaggregation of Revenue [Line Items]
Net sales	$ 1,592.6	$ 1,641.6	$ 5,070.0	$ 4,944.3
Percentage of Total Net Sales	25.60%	31.00%	27.70%	32.30%
Netcomm Products
Disaggregation of Revenue [Line Items]
Net sales	$ 721.0	$ 501.7	$ 1,912.6	$ 1,442.2
Percentage of Total Net Sales	11.60%	9.50%	10.40%	9.40%
Desktops
Disaggregation of Revenue [Line Items]
Net sales	$ 333.9	$ 316.1	$ 1,021.5	$ 873.5
Percentage of Total Net Sales	5.40%	6.00%	5.60%	5.70%
Video
Disaggregation of Revenue [Line Items]
Net sales	$ 441.4	$ 424.0	$ 1,453.9	$ 1,161.7
Percentage of Total Net Sales	7.10%	8.00%	7.90%	7.60%
Enterprise and Data Storage (Including Drives)
Disaggregation of Revenue [Line Items]
Net sales	$ 376.9	$ 228.1	$ 1,053.9	$ 730.2
Percentage of Total Net Sales	6.10%	4.30%	5.80%	4.80%
Other Hardware
Disaggregation of Revenue [Line Items]
Net sales	$ 1,346.9	$ 1,152.2	$ 3,704.8	$ 3,308.4
Percentage of Total Net Sales	21.70%	21.70%	20.20%	21.60%
Software
Disaggregation of Revenue [Line Items]
Net sales	$ 884.2	$ 717.7	$ 2,603.6	$ 1,959.2
Percentage of Total Net Sales	14.20%	13.50%	14.20%	12.80%
Software | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 355.1	$ 279.3	$ 1,177.9	$ 813.9
Software | Small Business
Disaggregation of Revenue [Line Items]
Net sales	62.4	50.2	177.2	148.7
Software | Public
Disaggregation of Revenue [Line Items]
Net sales	346.8	312.9	888.8	745.4
Software | Other
Disaggregation of Revenue [Line Items]
Net sales	119.9	75.3	359.7	251.2
Services
Disaggregation of Revenue [Line Items]
Net sales	$ 486.9	$ 286.9	$ 1,394.0	$ 772.4
Percentage of Total Net Sales	7.80%	5.40%	7.60%	5.10%
Services | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 245.8	$ 128.5	$ 700.0	$ 342.0
Services | Small Business
Disaggregation of Revenue [Line Items]
Net sales	24.0	10.4	58.9	31.9
Services | Public
Disaggregation of Revenue [Line Items]
Net sales	151.1	89.2	432.6	217.2
Services | Other
Disaggregation of Revenue [Line Items]
Net sales	66.0	58.8	202.5	181.3
Other
Disaggregation of Revenue [Line Items]
Net sales	$ 31.7	$ 31.7	$ 96.1	$ 92.0
Percentage of Total Net Sales	0.50%	0.60%	0.60%	0.70%
Other | Corporate
Disaggregation of Revenue [Line Items]
Net sales	$ 18.8	$ 18.3	$ 57.2	$ 51.7
Other | Small Business
Disaggregation of Revenue [Line Items]
Net sales	5.3	5.8	16.4	16.8
Other | Public
Disaggregation of Revenue [Line Items]
Net sales	5.0	4.5	14.1	13.2
Other | Other
Disaggregation of Revenue [Line Items]
Net sales	2.6	3.1	8.4	10.3
United States
Disaggregation of Revenue [Line Items]
Net sales	5,491.9	4,691.0	16,072.8	13,398.0
United States | Corporate
Disaggregation of Revenue [Line Items]
Net sales	2,570.8	2,064.6	7,843.0	5,844.3
United States | Small Business
Disaggregation of Revenue [Line Items]
Net sales	491.2	467.1	1,515.2	1,382.7
United States | Public
Disaggregation of Revenue [Line Items]
Net sales	2,424.3	2,153.9	6,700.3	6,156.3
United States | Other
Disaggregation of Revenue [Line Items]
Net sales	5.6	5.4	14.3	14.7
Rest of World
Disaggregation of Revenue [Line Items]
Net sales	723.6	609.0	2,237.6	1,885.9
Rest of World | Corporate
Disaggregation of Revenue [Line Items]
Net sales	7.0	2.7	23.1	11.9
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	$ 716.6	$ 606.3	$ 2,214.5	$ 1,874.0