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	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 8,434	$ 8,062	$ 8,112	$ 8,405	$ 7,769	$ 7,258	$ 7,249	$ 7,406	$ 33,013	$ 29,682	$ 28,035
Equity in earnings of affiliates									36	258	282
Adjusted segment EBITDA									6,531	6,061	5,868
Depreciation and amortization									1,679	1,465	1,421
Assets	28,075				26,898				28,075	26,898
Beginning Balance				5,251					5,251
Goodwill, Acquisitions									288
Goodwill, Dispositions									(3)
Goodwill, Foreign currency translation and other									3	16
Ending Balance	5,539				5,251				5,539	5,251
Interest expense									1,798	2,037	2,097
Gains on sales of facilities	(6)	(5)	(1)	(1)	(84)	(1)	(1)	(2)	(15)	(142)	(4)
Legal claim costs	110								175
Gain on acquisition of controlling interest in equity investment					(1,424)					(1,522)
Impairments of long-lived assets											123
Losses on retirement of debt						256	47			481
Termination of management agreement								149		181
Income before income taxes									2,894	3,561	2,231
National Group [Member]
Segment Reporting Information [Line Items]
Revenues									12,809	12,224	11,624
Equity in earnings of affiliates									(8)	(7)	(4)
Adjusted segment EBITDA									2,731	2,531	2,431
Depreciation and amortization									561	512	508
Assets	7,770				7,827				7,770	7,827
Beginning Balance				800					800
Goodwill, Acquisitions									46
Goodwill, Dispositions									(3)
Goodwill, Foreign currency translation and other									(1)
Ending Balance	842				800				842	800
Southwest Group [Member]
Segment Reporting Information [Line Items]
Revenues									11,506	9,311	8,700
Equity in earnings of affiliates									(27)	(251)	(277)
Adjusted segment EBITDA									2,734	2,370	2,254
Depreciation and amortization									595	464	427
Assets	10,197				9,908				10,197	9,908
Beginning Balance				3,160					3,160
Goodwill, Acquisitions									197
Ending Balance	3,357				3,160				3,357	3,160
Central Group [Member]
Segment Reporting Information [Line Items]
Revenues									7,305	6,982	6,727
Equity in earnings of affiliates									(2)		(1)
Adjusted segment EBITDA									1,431	1,285	1,272
Depreciation and amortization									354	347	352
Assets	5,227				5,187				5,227	5,187
Beginning Balance				1,019					1,019
Goodwill, Acquisitions									5
Ending Balance	1,024				1,019				1,024	1,019
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues									1,393	1,165	984
Equity in earnings of affiliates									1
Adjusted segment EBITDA									(365)	(125)	(89)
Depreciation and amortization									169	142	134
Assets	4,881				3,976				4,881	3,976
Beginning Balance				272					272
Goodwill, Acquisitions									40
Goodwill, Foreign currency translation and other									4
Ending Balance	316				272				316	272
Structure Subsequent to Year End [Member]
Segment Reporting Information [Line Items]
Beginning Balance				5,251					5,251
Goodwill, Acquisitions									288
Goodwill, Dispositions									(3)
Goodwill, Foreign currency translation and other									3
Ending Balance	5,539								5,539
Structure Subsequent to Year End [Member] | National Group [Member]
Segment Reporting Information [Line Items]
Revenues									15,505	14,741	13,964
Equity in earnings of affiliates									(9)	(7)	(4)
Adjusted segment EBITDA									3,325	3,052	2,890
Depreciation and amortization									694	639	624
Assets	9,451				9,551				9,451	9,551
Beginning Balance				991					991
Goodwill, Acquisitions									48
Goodwill, Dispositions									(3)
Goodwill, Foreign currency translation and other									(1)
Ending Balance	1,035				991				1,035	991
Structure Subsequent to Year End [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues									1,393	1,227	1,085
Equity in earnings of affiliates									1		(1)
Adjusted segment EBITDA									(369)	(132)	(105)
Depreciation and amortization									169	146	144
Assets	4,880				3,941				4,880	3,941
Beginning Balance				272					272
Goodwill, Acquisitions									39
Goodwill, Foreign currency translation and other									4
Ending Balance	315				272				315	272
Structure Subsequent to Year End [Member] | American Group [Member]
Segment Reporting Information [Line Items]
Revenues									16,115	13,714	12,986
Equity in earnings of affiliates									(28)	(251)	(277)
Adjusted segment EBITDA									3,575	3,141	3,083
Depreciation and amortization									816	680	653
Assets	13,744				13,406				13,744	13,406
Beginning Balance				3,988					3,988
Goodwill, Acquisitions									201
Ending Balance	$ 4,189				$ 3,988				$ 4,189	$ 3,988