Guarantor and Non-Guarantor Supplemental Financial Information - Condensed Consolidating Balance Sheet Information (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	$ 7,794	$ 5,540
Investment in subsidiaries	0	0
Intangible assets, net	2,157	2,309
Goodwill	8,139	8,229
Other assets, net	2,464	2,438
TOTAL ASSETS	20,554	18,516
Total current liabilities	10,497	7,879
Long-term debt, excluding current maturities	3,731	3,749
Other long-term liabilities	754	737
Redeemable non-controlling interests	20	22
Stockholders’ equity	5,552	6,129
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	20,554	18,516
Reportable Legal Entities | Parent
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	382	359
Investment in subsidiaries	10,102	10,265
Intangible assets, net	0	0
Goodwill	0	0
Other assets, net	0	5
TOTAL ASSETS	10,484	10,629
Total current liabilities	1,201	751
Long-term debt, excluding current maturities	3,731	3,749
Other long-term liabilities	0	0
Redeemable non-controlling interests	0	0
Stockholders’ equity	5,552	6,129
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	10,484	10,629
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	5,831	3,493
Investment in subsidiaries	4,239	4,249
Intangible assets, net	1,647	1,736
Goodwill	6,366	6,366
Other assets, net	1,692	1,677
TOTAL ASSETS	19,775	17,521
Total current liabilities	9,204	6,798
Long-term debt, excluding current maturities	0	0
Other long-term liabilities	500	494
Redeemable non-controlling interests	9	9
Stockholders’ equity	10,062	10,220
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	19,775	17,521
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	2,619	2,263
Investment in subsidiaries	0	0
Intangible assets, net	510	573
Goodwill	1,773	1,863
Other assets, net	791	775
TOTAL ASSETS	5,693	5,474
Total current liabilities	1,130	905
Long-term debt, excluding current maturities	0	0
Other long-term liabilities	273	262
Redeemable non-controlling interests	11	13
Stockholders’ equity	4,279	4,294
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	5,693	5,474
Eliminations
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	(1,038)	(575)
Investment in subsidiaries	(14,341)	(14,514)
Intangible assets, net	0	0
Goodwill	0	0
Other assets, net	(19)	(19)
TOTAL ASSETS	(15,398)	(15,108)
Total current liabilities	(1,038)	(575)
Long-term debt, excluding current maturities	0	0
Other long-term liabilities	(19)	(19)
Redeemable non-controlling interests	0	0
Stockholders’ equity	(14,341)	(14,514)
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ (15,398)	$ (15,108)