Financial Information for Guarantor Subsidiaries and Non-Guarantor Subsidiaries - Supplemental Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 113.5	$ 788.8
Restricted cash	37.1	29.0
Accounts receivable, net	526.7	540.9
Notes receivable, net	124.4	143.5
Inventories	238.4	243.1
Prepaid expenses, deposits and other current assets	269.7	131.1
Property and equipment, net	542.4	568.2
Investment in subsidiaries	0.0	0.0
Goodwill	3,308.2	2,956.1
Intangible assets, net	1,725.7	1,604.6
Intercompany balances	0.0	0.0
Software, net	301.2	339.4
Other assets	341.6	380.6
Total assets	7,528.9	7,725.3
Liabilities and stockholders' (deficit) equity
Current portion of long-term debt	46.8	40.3
Other current liabilities	1,025.6	699.5
Long-term debt, excluding current portion	8,735.0	8,736.3
Other long-term liabilities	340.1	276.2
Intercompany balances	0.0	0.0
Stockholders' (deficit) equity	(2,618.6)	(2,027.0)
Total liabilities and stockholders' (deficit) equity	7,528.9	7,725.3
Non-current restricted cash	15.2	16.3
Reportable Legal Entities | SGI (Issuer)
Assets
Cash and cash equivalents	0.0	0.0
Restricted cash	0.6	0.6
Accounts receivable, net	58.0	68.1
Notes receivable, net	0.0	0.0
Inventories	39.0	40.7
Prepaid expenses, deposits and other current assets	76.8	30.3
Property and equipment, net	112.1	91.5
Investment in subsidiaries	950.0	867.9
Goodwill	240.2	240.3
Intangible assets, net	34.3	34.9
Intercompany balances	5,812.7	5,889.8
Software, net	38.1	24.7
Other assets	413.1	388.8
Total assets	7,774.9	7,677.6
Liabilities and stockholders' (deficit) equity
Current portion of long-term debt	41.8	32.8
Other current liabilities	195.5	199.0
Long-term debt, excluding current portion	8,734.1	8,733.0
Other long-term liabilities	8.7	11.3
Intercompany balances	0.0	0.0
Stockholders' (deficit) equity	(1,205.2)	(1,298.5)
Total liabilities and stockholders' (deficit) equity	7,774.9	7,677.6
Reportable Legal Entities | SGC (Parent)
Assets
Cash and cash equivalents	38.6	732.6
Restricted cash	0.0	0.0
Accounts receivable, net	0.0	0.4
Notes receivable, net	0.0	0.0
Inventories	0.0	0.0
Prepaid expenses, deposits and other current assets	12.6	6.5
Property and equipment, net	32.4	28.8
Investment in subsidiaries	2,996.9	3,098.7
Goodwill	0.0	0.0
Intangible assets, net	10.8	15.7
Intercompany balances	0.0	0.0
Software, net	61.9	67.2
Other assets	234.2	234.4
Total assets	3,387.4	4,184.3
Liabilities and stockholders' (deficit) equity
Current portion of long-term debt	0.0	0.0
Other current liabilities	417.6	67.6
Long-term debt, excluding current portion	0.0	0.0
Other long-term liabilities	93.4	68.8
Intercompany balances	5,495.0	6,074.9
Stockholders' (deficit) equity	(2,618.6)	(2,027.0)
Total liabilities and stockholders' (deficit) equity	3,387.4	4,184.3
Reportable Legal Entities | Guarantor Subsidiaries
Assets
Cash and cash equivalents	0.0	0.0
Restricted cash	31.0	28.3
Accounts receivable, net	189.3	192.6
Notes receivable, net	109.6	121.1
Inventories	88.7	91.8
Prepaid expenses, deposits and other current assets	102.0	41.6
Property and equipment, net	232.6	295.6
Investment in subsidiaries	1,025.7	987.7
Goodwill	1,886.1	1,880.4
Intangible assets, net	1,199.4	1,335.3
Intercompany balances	27.8	0.0
Software, net	142.7	199.0
Other assets	48.2	62.0
Total assets	5,083.1	5,235.4
Liabilities and stockholders' (deficit) equity
Current portion of long-term debt	0.0	0.0
Other current liabilities	200.4	254.2
Long-term debt, excluding current portion	0.0	0.0
Other long-term liabilities	610.3	650.3
Intercompany balances	0.0	37.4
Stockholders' (deficit) equity	4,272.4	4,293.5
Total liabilities and stockholders' (deficit) equity	5,083.1	5,235.4
Non-current restricted cash	14.5	16.1
Reportable Legal Entities | Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	79.9	59.4
Restricted cash	5.5	0.1
Accounts receivable, net	279.4	279.8
Notes receivable, net	14.8	22.4
Inventories	130.7	131.8
Prepaid expenses, deposits and other current assets	78.1	52.7
Property and equipment, net	196.5	179.9
Investment in subsidiaries	0.0	0.0
Goodwill	1,181.9	835.4
Intangible assets, net	481.2	218.7
Intercompany balances	0.0	222.5
Software, net	58.5	48.5
Other assets	228.7	270.3
Total assets	2,735.2	2,321.5
Liabilities and stockholders' (deficit) equity
Current portion of long-term debt	5.0	7.5
Other current liabilities	249.0	206.4
Long-term debt, excluding current portion	0.9	3.3
Other long-term liabilities	197.6	110.9
Intercompany balances	345.5	0.0
Stockholders' (deficit) equity	1,937.2	1,993.4
Total liabilities and stockholders' (deficit) equity	2,735.2	2,321.5
Non-current restricted cash	0.7	0.7
Eliminating Entries
Assets
Cash and cash equivalents	(5.0)	(3.2)
Restricted cash	0.0	0.0
Accounts receivable, net	0.0	0.0
Notes receivable, net	0.0	0.0
Inventories	(20.0)	(21.2)
Prepaid expenses, deposits and other current assets	0.2	0.0
Property and equipment, net	(31.2)	(27.6)
Investment in subsidiaries	(4,972.6)	(4,954.3)
Goodwill	0.0	0.0
Intangible assets, net	0.0	0.0
Intercompany balances	(5,840.5)	(6,112.3)
Software, net	0.0	0.0
Other assets	(582.6)	(574.9)
Total assets	(11,451.7)	(11,693.5)
Liabilities and stockholders' (deficit) equity
Current portion of long-term debt	0.0	0.0
Other current liabilities	(36.9)	(27.7)
Long-term debt, excluding current portion	0.0	0.0
Other long-term liabilities	(569.9)	(565.1)
Intercompany balances	(5,840.5)	(6,112.3)
Stockholders' (deficit) equity	(5,004.4)	(4,988.4)
Total liabilities and stockholders' (deficit) equity	$ (11,451.7)	$ (11,693.5)