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, unless otherwise specified	0 Months Ended		3 Months Ended									12 Months Ended
	Nov. 30, 2014	Apr. 30, 2014	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues			$ 9,636	$ 9,220	$ 9,230	$ 8,832	$ 8,836	$ 8,456	$ 8,450	$ 8,440		$ 36,918	$ 34,182	$ 33,013
Equity in earnings of affiliates												(43)	(29)	(36)
Adjusted segment EBITDA												7,428	6,574	6,531
Depreciation and amortization												1,820	1,753	1,679
Depreciation and amortization												1,820	1,753	1,679
Interest expense												1,743	1,848	1,798
Losses (gains) on sales of facilities			(7)	(9)	(7)	(13)	(2)	1	(3)	11		(29)	10	(15)
Losses on retirement of debt	109	226	(68)		143	(49)				17		335	17
Legal claim costs						78				(11)	175	78		175
Income before income taxes												3,481	2,946	2,894
Assets			31,199				28,831				28,075	31,199	28,831	28,075
Goodwill and other intangible assets, Beginning Balance						5,903				5,539		5,903	5,539	5,251
Goodwill and other intangible assets, Acquisitions												548	378	288
Goodwill and other intangible assets, Foreign currency translation and other												(35)	(14)
Goodwill and other intangible assets, Ending Balance			6,416				5,903				5,539	6,416	5,903	5,539
National Group [Member]
Segment Reporting Information [Line Items]
Revenues												17,325	15,968	15,505
Equity in earnings of affiliates												(15)	(9)	(9)
Adjusted segment EBITDA												3,847	3,301	3,325
Depreciation and amortization												749	718	694
Depreciation and amortization												749	718	694
Assets			10,588				10,206				9,451	10,588	10,206	9,451
Goodwill and other intangible assets, Beginning Balance						1,104				1,035		1,104	1,035	991
Goodwill and other intangible assets, Acquisitions												72	68	48
Goodwill and other intangible assets, Foreign currency translation and other												(6)	1	(4)
Goodwill and other intangible assets, Ending Balance			1,170				1,104				1,035	1,170	1,104	1,035
American Group [Member]
Segment Reporting Information [Line Items]
Revenues												17,532	16,487	16,115
Equity in earnings of affiliates												(31)	(24)	(28)
Adjusted segment EBITDA												4,025	3,662	3,575
Depreciation and amortization												840	835	816
Depreciation and amortization												840	835	816
Assets			15,091				13,911				13,744	15,091	13,911	13,744
Goodwill and other intangible assets, Beginning Balance						4,190				4,189		4,190	4,189	3,988
Goodwill and other intangible assets, Acquisitions												428	13	200
Goodwill and other intangible assets, Foreign currency translation and other												(4)	(12)	1
Goodwill and other intangible assets, Ending Balance			4,614				4,190				4,189	4,614	4,190	4,189
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues												2,061	1,727	1,393
Equity in earnings of affiliates												3	4	1
Adjusted segment EBITDA												(444)	(389)	(369)
Depreciation and amortization												231	200	169
Depreciation and amortization												231	200	169
Assets			5,520				4,714				4,880	5,520	4,714	4,880
Goodwill and other intangible assets, Beginning Balance						609				315		609	315	272
Goodwill and other intangible assets, Acquisitions												48	297	40
Goodwill and other intangible assets, Foreign currency translation and other												(25)	(3)	3
Goodwill and other intangible assets, Ending Balance			$ 632				$ 609				$ 315	$ 632	$ 609	$ 315