Guarantor and Non-Guarantor Supplemental Financial Information - Schedule of Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Total current assets	$ 5,197	$ 5,540
Investment in subsidiaries	0	0
Intangible assets, net	1,992	2,309
Goodwill	8,120	8,229	$ 7,942
Other assets, net	2,724	2,438
TOTAL ASSETS	18,033	18,516
LIABILITIES AND STOCKHOLDERS’ EQUITY
Total current liabilities	8,060	7,879
Long-term debt, excluding current maturities	3,717	3,749
Other long-term liabilities	575	737
Redeemable non-controlling interests	30	22	0	$ 658
Stockholders’ equity	5,651	6,129	$ 5,693	$ 4,930
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	18,033	18,516
Reportable Legal Entities | Parent
ASSETS
Total current assets	402	359
Investment in subsidiaries	10,615	10,265
Intangible assets, net	0	0
Goodwill	0	0
Other assets, net	0	5
TOTAL ASSETS	11,017	10,629
LIABILITIES AND STOCKHOLDERS’ EQUITY
Total current liabilities	1,649	751
Long-term debt, excluding current maturities	3,717	3,749
Other long-term liabilities	0	0
Redeemable non-controlling interests	0	0
Stockholders’ equity	5,651	6,129
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	11,017	10,629
Reportable Legal Entities | Guarantor Subsidiaries
ASSETS
Total current assets	5,261	3,493
Investment in subsidiaries	3,425	4,249
Intangible assets, net	1,520	1,736
Goodwill	6,366	6,366
Other assets, net	1,840	1,677
TOTAL ASSETS	18,412	17,521
LIABILITIES AND STOCKHOLDERS’ EQUITY
Total current liabilities	7,396	6,798
Long-term debt, excluding current maturities	0	0
Other long-term liabilities	320	494
Redeemable non-controlling interests	17	9
Stockholders’ equity	10,679	10,220
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	18,412	17,521
Reportable Legal Entities | Non-Guarantor Subsidiaries
ASSETS
Total current assets	2,137	2,263
Investment in subsidiaries	0	0
Intangible assets, net	472	573
Goodwill	1,754	1,863
Other assets, net	913	775
TOTAL ASSETS	5,276	5,474
LIABILITIES AND STOCKHOLDERS’ EQUITY
Total current liabilities	1,618	905
Long-term debt, excluding current maturities	0	0
Other long-term liabilities	284	262
Redeemable non-controlling interests	13	13
Stockholders’ equity	3,361	4,294
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	5,276	5,474
Eliminations
ASSETS
Total current assets	(2,603)	(575)
Investment in subsidiaries	(14,040)	(14,514)
Intangible assets, net	0	0
Goodwill	0	0
Other assets, net	(29)	(19)
TOTAL ASSETS	(16,672)	(15,108)
LIABILITIES AND STOCKHOLDERS’ EQUITY
Total current liabilities	(2,603)	(575)
Long-term debt, excluding current maturities	0	0
Other long-term liabilities	(29)	(19)
Redeemable non-controlling interests	0	0
Stockholders’ equity	(14,040)	(14,514)
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ (16,672)	$ (15,108)