Segment and Geographic Information - Schedule of Geographic Distributions of Revenues, Equity in Earnings of Affiliates, Adjusted Segment EBITDA, Depreciation and Amortization and Assets (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 10,641	$ 10,270	$ 10,319	$ 10,260	$ 10,249	$ 9,856	$ 9,897	$ 9,676	$ 41,490	$ 39,678	$ 36,918
Equity in earnings of affiliates									54	46	43
Adjusted segment EBITDA									8,218	7,915	7,428
Depreciation and amortization									1,966	1,904	1,820
Interest expense									1,707	1,665	1,743
Losses (gains) on sales of facilities	(15)	(2)	$ (4)	2	4	$ 2	3	(6)	(23)	5	(29)
Losses on retirement of debt		$ 2			7		$ 79		4	135	335
Legal claim costs (benefits)									(246)	249	78
Income before income taxes									4,810	3,957	3,481
Assets	33,758				32,744				33,758	32,744	30,980
Goodwill and other intangible assets, Beginning Balance				$ 6,731				6,731	6,731	6,731	6,416	$ 5,903
Goodwill and other intangible assets, Acquisitions										41	345	548
Goodwill and other intangible assets, Foreign currency translation and other											(30)	(35)
Goodwill and other intangible assets, Sales, foreign currency translation, amortization and other										(68)
Goodwill and other intangible assets, Ending Balance	6,704				6,731				6,704	6,731	6,731	6,416
National Group [Member]
Segment Reporting Information [Line Items]
Revenues									19,845	18,756	17,335
Equity in earnings of affiliates									(20)	(7)	(15)
Adjusted segment EBITDA									4,565	4,271	3,848
Depreciation and amortization									806	769	749
Assets	12,320				11,332				12,320	11,332	10,590
Goodwill and other intangible assets, Beginning Balance								1,481		1,481	1,170	1,104
Goodwill and other intangible assets, Acquisitions											318	72
Goodwill and other intangible assets, Foreign currency translation and other											(7)	(6)
Goodwill and other intangible assets, Sales, foreign currency translation, amortization and other										(23)
Goodwill and other intangible assets, Ending Balance	1,458								1,458		1,481	1,170
American Group [Member]
Segment Reporting Information [Line Items]
Revenues									19,648	18,872	17,532
Equity in earnings of affiliates									(38)	(32)	(31)
Adjusted segment EBITDA									4,177	4,207	4,025
Depreciation and amortization									905	886	840
Assets	16,199				15,240				16,199	15,240	15,091
Goodwill and other intangible assets, Beginning Balance								4,638		4,638	4,614	4,190
Goodwill and other intangible assets, Acquisitions										33	27	428
Goodwill and other intangible assets, Foreign currency translation and other											(3)	(4)
Goodwill and other intangible assets, Sales, foreign currency translation, amortization and other										(10)
Goodwill and other intangible assets, Ending Balance	4,661								4,661		4,638	4,614
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues									1,997	2,050	2,051
Equity in earnings of affiliates									4	(7)	3
Adjusted segment EBITDA									(524)	(563)	(445)
Depreciation and amortization									255	249	231
Assets	5,239				$ 6,172				5,239	6,172	5,299
Goodwill and other intangible assets, Beginning Balance								$ 612		612	632	609
Goodwill and other intangible assets, Acquisitions										8		48
Goodwill and other intangible assets, Foreign currency translation and other											(20)	(25)
Goodwill and other intangible assets, Sales, foreign currency translation, amortization and other										$ (35)
Goodwill and other intangible assets, Ending Balance	$ 585								$ 585		$ 612	$ 632