Segment Information - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Total Net sales	$ 5,976.6	$ 5,423.4	$ 11,175.7	$ 10,296.1
Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	5,162.6	4,671.8	9,579.0	8,840.6
Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	408.4	392.7	818.6	766.0
Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	405.6	358.9	778.1	689.5
Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,581.5	2,195.2	4,817.5	4,331.1
Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	431.3	382.9	835.9	763.8
Government
Disaggregation of Revenue [Line Items]
Total Net sales	656.5	639.1	1,194.3	1,182.4
Education
Disaggregation of Revenue [Line Items]
Total Net sales	906.7	1,017.4	1,559.1	1,614.2
Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	728.5	586.8	1,416.4	1,171.4
Other
Disaggregation of Revenue [Line Items]
Total Net sales	672.1	602.0	1,352.5	1,233.2
Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	4,442.0	4,061.9	8,186.3	7,608.0
Software
Disaggregation of Revenue [Line Items]
Total Net sales	990.2	855.6	1,938.5	1,730.0
Services
Disaggregation of Revenue [Line Items]
Total Net sales	515.2	478.4	994.5	904.2
Other
Disaggregation of Revenue [Line Items]
Total Net sales	29.2	27.5	56.4	53.9
Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,581.5	2,195.2	4,817.5	4,331.1
Corporate | Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	2,193.5	1,830.4	4,044.2	3,609.7
Corporate | Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	204.6	193.2	417.4	388.0
Corporate | Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	183.4	171.6	355.9	333.4
Corporate | Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,581.5	2,195.2	4,817.5	4,331.1
Corporate | Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate | Government
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate | Education
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate | Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate | Other
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Corporate | Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	1,839.9	1,532.2	3,353.8	2,997.8
Corporate | Software
Disaggregation of Revenue [Line Items]
Total Net sales	486.6	416.2	967.9	853.7
Corporate | Services
Disaggregation of Revenue [Line Items]
Total Net sales	239.3	231.2	464.6	449.2
Corporate | Other
Disaggregation of Revenue [Line Items]
Total Net sales	15.7	15.6	31.2	30.4
Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	431.3	382.9	835.9	763.8
Small Business | Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	378.1	337.2	732.9	668.9
Small Business | Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	36.5	34.2	71.5	73.3
Small Business | Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	16.7	11.5	31.5	21.6
Small Business | Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business | Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	431.3	382.9	835.9	763.8
Small Business | Government
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business | Education
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business | Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business | Other
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Small Business | Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	343.5	307.3	661.6	607.3
Small Business | Software
Disaggregation of Revenue [Line Items]
Total Net sales	60.5	53.5	122.0	113.4
Small Business | Services
Disaggregation of Revenue [Line Items]
Total Net sales	22.7	17.7	43.4	34.3
Small Business | Other
Disaggregation of Revenue [Line Items]
Total Net sales	4.6	4.4	8.9	8.8
Public
Disaggregation of Revenue [Line Items]
Total Net sales	2,291.7	2,243.3	4,169.8	3,968.0
Public | Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	2,030.9	1,992.2	3,667.2	3,507.9
Public | Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	124.8	134.5	246.1	242.7
Public | Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	136.0	116.6	256.5	217.4
Public | Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Public | Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Public | Government
Disaggregation of Revenue [Line Items]
Total Net sales	656.5	639.1	1,194.3	1,182.4
Public | Education
Disaggregation of Revenue [Line Items]
Total Net sales	906.7	1,017.4	1,559.1	1,614.2
Public | Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	728.5	586.8	1,416.4	1,171.4
Public | Other
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Public | Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	1,781.8	1,796.2	3,189.0	3,112.6
Public | Software
Disaggregation of Revenue [Line Items]
Total Net sales	333.7	288.7	644.4	565.6
Public | Services
Disaggregation of Revenue [Line Items]
Total Net sales	171.8	153.6	327.6	280.6
Public | Other
Disaggregation of Revenue [Line Items]
Total Net sales	4.4	4.8	8.8	9.2
Other
Disaggregation of Revenue [Line Items]
Total Net sales	672.1	602.0	1,352.5	1,233.2
Other | Transferred at a point in time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	560.1	512.0	1,134.7	1,054.1
Other | Transferred at a point in time where CDW is agent
Disaggregation of Revenue [Line Items]
Total Net sales	42.5	30.8	83.6	62.0
Other | Transferred over time where CDW is principal
Disaggregation of Revenue [Line Items]
Total Net sales	69.5	59.2	134.2	117.1
Other | Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other | Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other | Government
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other | Education
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other | Healthcare
Disaggregation of Revenue [Line Items]
Total Net sales	0.0	0.0	0.0	0.0
Other | Other
Disaggregation of Revenue [Line Items]
Total Net sales	672.1	602.0	1,352.5	1,233.2
Other | Hardware
Disaggregation of Revenue [Line Items]
Total Net sales	476.8	426.2	981.9	890.3
Other | Software
Disaggregation of Revenue [Line Items]
Total Net sales	109.4	97.2	204.2	197.3
Other | Services
Disaggregation of Revenue [Line Items]
Total Net sales	81.4	75.9	158.9	140.1
Other | Other
Disaggregation of Revenue [Line Items]
Total Net sales	4.5	2.7	7.5	5.5
United States
Disaggregation of Revenue [Line Items]
Total Net sales	5,278.6	4,809.1	9,770.2	9,029.7
United States | Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	2,560.0	2,182.7	4,771.7	4,298.6
United States | Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	423.5	376.9	822.5	752.9
United States | Public
Disaggregation of Revenue [Line Items]
Total Net sales	2,289.7	2,242.0	4,164.9	3,964.8
United States | Other
Disaggregation of Revenue [Line Items]
Total Net sales	5.4	7.5	11.1	13.4
Rest of World
Disaggregation of Revenue [Line Items]
Total Net sales	698.0	614.3	1,405.5	1,266.4
Rest of World | Corporate
Disaggregation of Revenue [Line Items]
Total Net sales	21.5	12.5	45.8	32.5
Rest of World | Small Business
Disaggregation of Revenue [Line Items]
Total Net sales	7.8	6.0	13.4	10.9
Rest of World | Public
Disaggregation of Revenue [Line Items]
Total Net sales	2.0	1.3	4.9	3.2
Rest of World | Other
Disaggregation of Revenue [Line Items]
Total Net sales	$ 666.7	$ 594.5	$ 1,341.4	$ 1,219.8