Supplemental Guarantor Information - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 221.0	$ 144.2	$ 251.7	$ 263.7
Accounts receivable, net	2,274.0	2,329.3
Merchandise inventory	485.8	411.5
Miscellaneous receivables	310.2	343.0
Prepaid expenses and other	188.9	168.3
Total current assets	3,479.9	3,396.3
Property and equipment, net	153.1	161.1
Goodwill	2,488.8	2,479.6
Other intangible assets, net	859.0	897.0
Other assets	47.1	32.7
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	7,027.9	6,966.7
Current liabilities:
Accounts payable-trade	1,288.5	1,317.7
Accounts payable-inventory financing	523.7	498.0
Current maturities of long-term debt	25.8	25.5
Contract liabilities	193.6	158.8
Accrued expenses and other current liabilities	550.9	522.1
Total current liabilities	2,582.5	2,522.1
Long-term liabilities:
Debt	3,209.7	3,210.0
Deferred income taxes	188.9	196.3
Other liabilities	49.9	52.7
Total long-term liabilities	3,448.5	3,459.0
Total stockholders' equity	996.9	982.9
Total stockholders' equity		985.6
Total Liabilities and Stockholders' Equity	7,027.9	6,966.7
Consolidating Adjustments
Current assets:
Cash and cash equivalents	(18.2)	(1.9)	(23.6)	0.0
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	(18.2)	(1.9)
Property and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Other assets	(216.9)	(211.6)
Investment in and advances to subsidiaries	(4,012.1)	(4,050.0)
Total Assets	(4,247.2)	(4,263.5)
Current liabilities:
Accounts payable-trade	(18.2)	(1.9)
Accounts payable-inventory financing	0.0	0.0
Current maturities of long-term debt	0.0	0.0
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	0.0	0.0
Total current liabilities	(18.2)	(1.9)
Long-term liabilities:
Debt	0.0	0.0
Deferred income taxes	(1.6)	(1.7)
Other liabilities	(215.3)	(209.9)
Total long-term liabilities	(216.9)	(211.6)
Total stockholders' equity	(4,012.1)
Total stockholders' equity		(4,050.0)
Total Liabilities and Stockholders' Equity	(4,247.2)	(4,263.5)
Parent Guarantor | Reportable Legal Entities
Current assets:
Cash and cash equivalents	0.0	0.0	0.0	0.0
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	0.0	0.0
Property and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Other assets	1.6	1.7
Investment in and advances to subsidiaries	995.3	983.9
Total Assets	996.9	985.6
Current liabilities:
Accounts payable-trade	0.0	0.0
Accounts payable-inventory financing	0.0	0.0
Current maturities of long-term debt	0.0	0.0
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	0.0	0.0
Total current liabilities	0.0	0.0
Long-term liabilities:
Debt	0.0	0.0
Deferred income taxes	0.0	0.0
Other liabilities	0.0	0.0
Total long-term liabilities	0.0	0.0
Total stockholders' equity	996.9
Total stockholders' equity		985.6
Total Liabilities and Stockholders' Equity	996.9	985.6
Subsidiary Issuer | Reportable Legal Entities
Current assets:
Cash and cash equivalents	173.3	113.7	204.9	222.7
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	105.2	103.9
Prepaid expenses and other	21.5	18.0
Total current assets	300.0	235.6
Property and equipment, net	87.7	95.0
Goodwill	751.8	751.8
Other intangible assets, net	277.4	280.1
Other assets	52.1	30.7
Investment in and advances to subsidiaries	3,016.8	3,066.1
Total Assets	4,485.8	4,459.3
Current liabilities:
Accounts payable-trade	24.6	42.5
Accounts payable-inventory financing	0.0	1.0
Current maturities of long-term debt	14.9	14.9
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	210.6	173.3
Total current liabilities	250.1	231.7
Long-term liabilities:
Debt	3,131.2	3,134.2
Deferred income taxes	69.0	66.5
Other liabilities	40.2	43.0
Total long-term liabilities	3,240.4	3,243.7
Total stockholders' equity	995.3
Total stockholders' equity		983.9
Total Liabilities and Stockholders' Equity	4,485.8	4,459.3
Guarantor Subsidiaries | Reportable Legal Entities
Current assets:
Cash and cash equivalents	0.0	0.0	0.0	3.1
Accounts receivable, net	1,898.8	2,015.7
Merchandise inventory	401.0	354.6
Miscellaneous receivables	182.7	211.1
Prepaid expenses and other	119.9	100.4
Total current assets	2,602.4	2,681.8
Property and equipment, net	42.1	43.5
Goodwill	1,439.0	1,439.0
Other intangible assets, net	388.6	424.5
Other assets	207.5	209.3
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	4,679.6	4,798.1
Current liabilities:
Accounts payable-trade	1,063.6	1,112.1
Accounts payable-inventory financing	481.8	480.9
Current maturities of long-term debt	3.8	3.8
Contract liabilities	100.4	87.5
Accrued expenses and other current liabilities	263.4	262.0
Total current liabilities	1,913.0	1,946.3
Long-term liabilities:
Debt	8.3	8.3
Deferred income taxes	89.3	100.1
Other liabilities	4.9	4.7
Total long-term liabilities	102.5	113.1
Total stockholders' equity	2,664.1
Total stockholders' equity		2,738.7
Total Liabilities and Stockholders' Equity	4,679.6	4,798.1
Non-Guarantor Subsidiaries | Reportable Legal Entities
Current assets:
Cash and cash equivalents	65.9	32.4	70.4	37.9
Accounts receivable, net	375.2	313.6
Merchandise inventory	84.8	56.9
Miscellaneous receivables	22.3	28.0
Prepaid expenses and other	47.5	49.9
Total current assets	595.7	480.8
Property and equipment, net	23.3	22.6
Goodwill	298.0	288.8
Other intangible assets, net	193.0	192.4
Other assets	2.8	2.6
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	1,112.8	987.2
Current liabilities:
Accounts payable-trade	218.5	165.0
Accounts payable-inventory financing	41.9	16.1
Current maturities of long-term debt	7.1	6.8
Contract liabilities	93.2	71.3
Accrued expenses and other current liabilities	76.9	86.8
Total current liabilities	437.6	346.0
Long-term liabilities:
Debt	70.2	67.5
Deferred income taxes	32.2	31.4
Other liabilities	220.1	214.9
Total long-term liabilities	322.5	313.8
Total stockholders' equity	352.7
Total stockholders' equity		327.4
Total Liabilities and Stockholders' Equity	1,112.8	987.2
Co-Issuer | Reportable Legal Entities
Current assets:
Cash and cash equivalents	0.0	0.0	$ 0.0	$ 0.0
Accounts receivable, net	0.0	0.0
Merchandise inventory	0.0	0.0
Miscellaneous receivables	0.0	0.0
Prepaid expenses and other	0.0	0.0
Total current assets	0.0	0.0
Property and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Other intangible assets, net	0.0	0.0
Other assets	0.0	0.0
Investment in and advances to subsidiaries	0.0	0.0
Total Assets	0.0	0.0
Current liabilities:
Accounts payable-trade	0.0	0.0
Accounts payable-inventory financing	0.0	0.0
Current maturities of long-term debt	0.0	0.0
Contract liabilities	0.0	0.0
Accrued expenses and other current liabilities	0.0	0.0
Total current liabilities	0.0	0.0
Long-term liabilities:
Debt	0.0	0.0
Deferred income taxes	0.0	0.0
Other liabilities	0.0	0.0
Total long-term liabilities	0.0	0.0
Total stockholders' equity	0.0
Total stockholders' equity		0.0
Total Liabilities and Stockholders' Equity	$ 0.0	$ 0.0