Segment Information - Products and Services (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 4,956.2	$ 4,756.4	$ 4,365.7	$ 4,389.2	$ 4,536.9	$ 4,907.7	$ 4,629.9	$ 3,957.9	$ 18,467.5	$ 18,032.4	$ 16,240.5
Percentage of Total Net Sales									100.00%	100.00%	100.00%
Total Hardware
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 14,833.4	$ 14,482.2	$ 13,131.7
Percentage of Total Net Sales									80.20%	80.40%	80.90%
Notebooks/Mobile Devices
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 5,486.2	$ 4,344.9	$ 3,843.3
Percentage of Total Net Sales									29.70%	24.10%	23.70%
Netcomm Products
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 1,955.0	$ 2,189.1	$ 2,116.6
Percentage of Total Net Sales									10.60%	12.10%	13.00%
Desktops
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 1,132.4	$ 1,547.3	$ 1,254.9
Percentage of Total Net Sales									6.10%	8.60%	7.70%
Video
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 1,190.8	$ 1,272.9	$ 1,184.1
Percentage of Total Net Sales									6.40%	7.10%	7.30%
Enterprise and Data Storage (Including Drives)
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 947.4	$ 1,147.6	$ 1,102.4
Percentage of Total Net Sales									5.10%	6.40%	6.80%
Other Hardware
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 4,121.6	$ 3,980.4	$ 3,630.4
Percentage of Total Net Sales									22.30%	22.10%	22.40%
Software
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 2,581.0	$ 2,585.0	$ 2,299.1
Percentage of Total Net Sales									14.00%	14.30%	14.20%
Services
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 913.9	$ 840.9	$ 695.9
Percentage of Total Net Sales									4.90%	4.70%	4.30%
Other
Net Sales from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 139.2	$ 124.3	$ 113.8
Percentage of Total Net Sales									0.90%	0.60%	0.60%