Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) employee segment	Jun. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Number of operating segments which do not meet reportable unit quantitative threshold | segment			2
Net sales	$ 3,994.4	$ 3,664.6	$ 7,319.1	$ 6,781.3
Income (loss) from operations	231.1	223.5	400.9	384.5
Depreciation and amortization expense	(65.4)	(63.7)	(129.5)	(127.7)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	1,630.7	1,490.8	3,107.0	2,905.7
Income (loss) from operations	127.1	117.5	238.5	219.1
Depreciation and amortization expense	(20.8)	(20.7)	(41.7)	(41.4)
Operating Segments | Small Business
Segment Reporting Information [Line Items]
Net sales	321.5	288.4	620.2	565.7
Income (loss) from operations	19.3	17.7	36.0	34.3
Depreciation and amortization expense	(5.1)	(5.2)	(10.3)	(10.3)
Operating Segments | Public
Segment Reporting Information [Line Items]
Net sales	1,674.1	1,547.0	2,850.6	2,616.5
Income (loss) from operations	104.5	108.3	165.1	166.7
Depreciation and amortization expense	(11.2)	(11.1)	(22.4)	(22.3)
Operating Segments | Other
Segment Reporting Information [Line Items]
Net sales	368.1	338.4	741.3	693.4
Income (loss) from operations	12.6	9.4	25.2	17.5
Depreciation and amortization expense	(7.6)	(8.3)	(14.6)	(16.9)
Headquarters
Segment Reporting Information [Line Items]
Net sales	0.0	0.0	0.0	0.0
Income (loss) from operations	(32.4)	(29.4)	(63.9)	(53.1)
Depreciation and amortization expense	$ (20.7)	$ (18.4)	$ (40.5)	$ (36.8)
Minimum | Corporate
Segment Reporting Information [Line Items]
Customer segments, customer employee headcount | employee	250		250
Maximum | Small Business
Segment Reporting Information [Line Items]
Customer segments, customer employee headcount | employee	250		250