Segment Information - Schedule of Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 4,186.1	$ 3,891.7	$ 7,792.5	$ 7,147.6
Income (loss) from operations	265.5	230.8	469.6	401.5
Depreciation and amortization expense	(66.3)	(65.4)	(132.9)	(129.5)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	1,733.8	1,580.1	3,299.6	3,020.7
Income (loss) from operations	141.3	126.9	266.1	239.0
Depreciation and amortization expense	(20.4)	(20.8)	(41.5)	(41.7)
Operating Segments | Small Business
Segment Reporting Information [Line Items]
Net sales	329.5	315.0	657.1	607.0
Income (loss) from operations	24.6	19.4	46.9	36.0
Depreciation and amortization expense	(5.2)	(5.1)	(10.4)	(10.3)
Operating Segments | Public
Segment Reporting Information [Line Items]
Net sales	1,635.4	1,632.8	2,865.4	2,786.5
Income (loss) from operations	113.0	104.6	184.7	165.3
Depreciation and amortization expense	(11.3)	(11.2)	(22.5)	(22.4)
Operating Segments | Other
Segment Reporting Information [Line Items]
Net sales	487.4	363.8	970.4	733.4
Income (loss) from operations	21.7	12.5	41.5	25.1
Depreciation and amortization expense	(9.0)	(7.6)	(17.8)	(14.6)
Headquarters
Segment Reporting Information [Line Items]
Net sales	0.0	0.0	0.0	0.0
Income (loss) from operations	(35.1)	(32.6)	(69.6)	(63.9)
Depreciation and amortization expense	$ (20.4)	$ (20.7)	$ (40.7)	$ (40.5)