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		9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Revenues		$ 8,456	$ 8,062	$ 25,346	$ 24,579
Equity in earnings of affiliates		(9)	(6)	(29)	(26)
Adjusted segment EBITDA		1,603	1,533	4,860	4,925
Depreciation and amortization		443	417	1,292	1,254
Adjusted segment EBITDA		1,603	1,533	4,860	4,925
Depreciation and amortization		443	417	1,292	1,254
Interest expense		458	446	1,392	1,336
Losses (gains) on sales of facilities		1	(7)	13	(4)
Loss on retirement of debt	17			17
Income before income taxes		701	677	2,146	2,339
National Group [Member]
Segment Reporting Information [Line Items]
Revenues		3,930	3,755	11,875	11,553
Equity in earnings of affiliates		(3)		(8)	(7)
Adjusted segment EBITDA		805	768	2,440	2,478
Depreciation and amortization		181	171	532	520
Adjusted segment EBITDA		805	768	2,440	2,478
Depreciation and amortization		181	171	532	520
American Group [Member]
Segment Reporting Information [Line Items]
Revenues		4,082	3,982	12,181	12,033
Equity in earnings of affiliates		(6)	(6)	(19)	(20)
Adjusted segment EBITDA		910	843	2,654	2,657
Depreciation and amortization		206	207	610	612
Adjusted segment EBITDA		910	843	2,654	2,657
Depreciation and amortization		206	207	610	612
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues		444	325	1,290	993
Equity in earnings of affiliates				(2)	1
Adjusted segment EBITDA		(112)	(78)	(234)	(210)
Depreciation and amortization		56	39	150	122
Adjusted segment EBITDA		(112)	(78)	(234)	(210)
Depreciation and amortization		$ 56	$ 39	$ 150	$ 122