Segment Information - Schedule of Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 3,606.4	$ 3,256.0
Income (loss) from operations	204.1	170.7
Depreciation and amortization expense	(66.6)	(64.2)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	1,565.8	1,440.6
Income (loss) from operations	124.8	112.1
Depreciation and amortization expense	(21.1)	(20.8)
Operating Segments | Small Business
Segment Reporting Information [Line Items]
Net sales	327.6	292.0
Income (loss) from operations	22.3	16.6
Depreciation and amortization expense	(5.2)	(5.1)
Operating Segments | Public
Segment Reporting Information [Line Items]
Net sales	1,230.0	1,153.7
Income (loss) from operations	71.7	60.8
Depreciation and amortization expense	(11.2)	(11.2)
Operating Segments | Other
Segment Reporting Information [Line Items]
Net sales	483.0	369.7
Income (loss) from operations	19.8	12.7
Depreciation and amortization expense	(8.8)	(7.2)
Headquarters
Segment Reporting Information [Line Items]
Net sales	0.0	0.0
Income (loss) from operations	(34.5)	(31.5)
Depreciation and amortization expense	$ (20.3)	$ (19.9)