Segment and Geographic Information - Schedule of Geographic Distributions of Revenues, Equity in Earnings of Affiliates, Adjusted Segment EBITDA and Depreciation and Amortization (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 9,230	$ 8,450			$ 18,062	$ 16,890
Equity in earnings of affiliates	(9)	(12)			(18)	(20)
Adjusted segment EBITDA	2,000	1,689			3,644	3,257
Depreciation and amortization	454	425			901	849
Interest expense	427	462			887	934
Losses (gains) on sales of facilities	(11)	(4)			(32)	12
Losses on retirement of debt	226		17		226	17
Legal claim costs				175	78
Income before income taxes	904	806			1,584	1,445
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,267	3,964			8,427	7,945
Equity in earnings of affiliates	(3)	(3)			(6)	(5)
Adjusted segment EBITDA	946	831			1,802	1,635
Depreciation and amortization	190	177			377	351
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,447	4,065			8,599	8,099
Equity in earnings of affiliates	(8)	(7)			(15)	(13)
Adjusted segment EBITDA	1,134	916			1,984	1,744
Depreciation and amortization	211	202			416	404
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	516	421			1,036	846
Equity in earnings of affiliates	2	(2)			3	(2)
Adjusted segment EBITDA	(80)	(58)			(142)	(122)
Depreciation and amortization	$ 53	$ 46			$ 108	$ 94