The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
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The net result for the period of deducting operating expenses from operating revenues.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Segment Information - Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 3,838.6	$ 4,033.9	$ 3,994.4	$ 3,324.7	$ 3,492.4	$ 3,708.2	$ 3,664.6	$ 3,116.7	$ 15,191.5	$ 13,981.9	$ 12,988.7
Income (loss) from operations	221.6	243.7	231.1	169.8	197.2	237.5	223.5	161.0	866.1	819.2	742.0
Depreciation and amortization expense									(260.9)	(254.5)	(227.4)
Corporate
Segment Reporting Information [Line Items]
Net sales	1,641.4	1,598.5	1,630.7	1,476.3	1,517.7	1,466.4	1,490.8	1,414.9
Small Business
Segment Reporting Information [Line Items]
Net sales	314.8	311.5	321.5	298.7	291.8	282.5	288.4	277.4
Other
Segment Reporting Information [Line Items]
Net sales	$ 428.3	$ 391.0	$ 368.1	$ 373.2	$ 350.5	$ 318.7	$ 338.4	$ 355.0
Operating Segments \| Corporate
Segment Reporting Information [Line Items]
Net sales									6,347.0	5,889.8	5,878.7
Income (loss) from operations									487.0	453.6	432.5
Depreciation and amortization expense									(83.1)	(82.9)	(82.6)
Operating Segments \| Small Business
Segment Reporting Information [Line Items]
Net sales									1,246.5	1,140.1	1,089.6
Income (loss) from operations									74.4	68.9	68.3
Depreciation and amortization expense									(20.7)	(20.6)	(20.6)
Operating Segments \| Public
Segment Reporting Information [Line Items]
Net sales									6,037.5	5,589.4	5,183.6
Income (loss) from operations									374.0	368.0	328.6
Depreciation and amortization expense									(44.8)	(44.7)	(44.7)
Operating Segments \| Other
Segment Reporting Information [Line Items]
Net sales									1,560.5	1,362.6	836.8
Income (loss) from operations									57.9	43.6	27.1
Depreciation and amortization expense									(30.9)	(32.1)	(16.2)
Headquarters
Segment Reporting Information [Line Items]
Net sales									0.0	0.0	0.0
Income (loss) from operations									(127.2)	(114.9)	(114.5)
Depreciation and amortization expense									$ (81.4)	$ (74.2)	$ (63.3)