Segment Information - Schedule of Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 4,629.9	$ 4,186.1	$ 8,587.8	$ 7,792.5
Income (loss) from operations	300.3	265.5	529.2	469.6
Depreciation and amortization expense	(65.0)	(66.3)	(129.3)	(132.9)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	1,883.9	1,733.8	3,620.1	3,299.6
Income (loss) from operations	157.2	139.7	291.9	262.6
Depreciation and amortization expense	21.6	22.0	(43.1)	(45.0)
Operating Segments | Small Business
Segment Reporting Information [Line Items]
Net sales	377.4	329.5	733.0	657.1
Income (loss) from operations	26.6	24.2	51.0	46.2
Depreciation and amortization expense	5.6	5.6	(11.2)	(11.1)
Operating Segments | Public
Segment Reporting Information [Line Items]
Net sales	1,840.1	1,635.4	3,170.8	2,865.4
Income (loss) from operations	129.4	111.5	205.5	181.7
Depreciation and amortization expense	13.7	12.8	(26.4)	(25.5)
Operating Segments | Other
Segment Reporting Information [Line Items]
Net sales	528.5	487.4	1,063.9	970.4
Income (loss) from operations	19.1	21.7	44.7	41.5
Depreciation and amortization expense	7.8	9.0	(15.2)	(17.8)
Headquarters
Segment Reporting Information [Line Items]
Net sales	0.0	0.0	0.0	0.0
Income (loss) from operations	(32.0)	(31.6)	(63.9)	(62.4)
Depreciation and amortization expense	$ 16.3	$ 16.9	$ (33.4)	$ (33.5)