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	1 Months Ended	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues		$ 8,836	$ 8,456	$ 8,450	$ 8,440	$ 8,434	$ 8,062	$ 8,112	$ 8,405	$ 34,182	$ 33,013	$ 29,682
Equity in earnings of affiliates										(29)	(36)	(258)
Adjusted segment EBITDA										6,574	6,531	6,061
Depreciation and amortization										1,753	1,679	1,465
Adjusted segment EBITDA										6,574	6,531	6,061
Depreciation and amortization										1,753	1,679	1,465
Interest expense										1,848	1,798	2,037
Losses (gains) on sales of facilities		(2)	1	(3)	11	(6)	(5)	1	1	10	(15)	(142)
Losses on retirement of debt	17				11					17		481
Legal claim costs						110					175
Gain on acquisition of controlling interest in equity investment												(1,522)
Termination of management agreement												181
Income before income taxes										2,946	2,894	3,561
Assets		28,831				28,075				28,831	28,075
Goodwill and other intangible assets, Beginning Balance					5,539					5,539
Goodwill and other intangible assets, Acquisitions										378
Goodwill and other intangible assets, Dispositions										(1)
Goodwill and other intangible assets, Foreign currency translation and other										(13)	3
Goodwill and other intangible assets, Ending Balance		5,903				5,539				5,903	5,539
National Group [Member]
Segment Reporting Information [Line Items]
Revenues										15,968	15,505	14,741
Equity in earnings of affiliates										(9)	(9)	(7)
Adjusted segment EBITDA										3,301	3,325	3,052
Depreciation and amortization										718	694	639
Adjusted segment EBITDA										3,301	3,325	3,052
Depreciation and amortization										718	694	639
Assets		10,206				9,451				10,206	9,451
Goodwill and other intangible assets, Beginning Balance					1,035					1,035
Goodwill and other intangible assets, Acquisitions										68
Goodwill and other intangible assets, Dispositions
Goodwill and other intangible assets, Foreign currency translation and other										1
Goodwill and other intangible assets, Ending Balance		1,104				1,035				1,104	1,035
American Group [Member]
Segment Reporting Information [Line Items]
Revenues										16,487	16,115	13,714
Equity in earnings of affiliates										(24)	(28)	(251)
Adjusted segment EBITDA										3,662	3,575	3,141
Depreciation and amortization										835	816	680
Adjusted segment EBITDA										3,662	3,575	3,141
Depreciation and amortization										835	816	680
Assets		13,911				13,744				13,911	13,744
Goodwill and other intangible assets, Beginning Balance					4,189					4,189
Goodwill and other intangible assets, Acquisitions										13
Goodwill and other intangible assets, Dispositions										(1)
Goodwill and other intangible assets, Foreign currency translation and other										(11)
Goodwill and other intangible assets, Ending Balance		4,190				4,189				4,190	4,189
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues										1,727	1,393	1,227
Equity in earnings of affiliates										4	1
Adjusted segment EBITDA										(389)	(369)	(132)
Depreciation and amortization										200	169	146
Adjusted segment EBITDA										(389)	(369)	(132)
Depreciation and amortization										200	169	146
Assets		4,714				4,880				4,714	4,880
Goodwill and other intangible assets, Beginning Balance					315					315
Goodwill and other intangible assets, Acquisitions										297
Goodwill and other intangible assets, Dispositions
Goodwill and other intangible assets, Foreign currency translation and other										(3)
Goodwill and other intangible assets, Ending Balance		$ 609				$ 315				$ 609	$ 315