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					9 Months Ended
	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 9,220		$ 8,456			$ 27,282	$ 25,346
Equity in earnings of affiliates	(14)		(9)			(32)	(29)
Adjusted segment EBITDA	1,828		1,603			5,472	4,860
Depreciation and amortization	460		443			1,361	1,292
Interest expense	427		458			1,314	1,392
Losses (gains) on sales of facilities	12		1			(20)	13
Losses on retirement of debt				17		226	17
Legal claim costs		78			175	78
Income before income taxes	929		701			2,513	2,146
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,387		3,930			12,814	11,875
Equity in earnings of affiliates	(6)		(3)			(12)	(8)
Adjusted segment EBITDA	1,008		805			2,810	2,440
Depreciation and amortization	187		181			564	532
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,319		4,082			12,918	12,181
Equity in earnings of affiliates	(8)		(6)			(23)	(19)
Adjusted segment EBITDA	927		910			2,911	2,654
Depreciation and amortization	210		206			626	610
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	514		444			1,550	1,290
Equity in earnings of affiliates						3	(2)
Adjusted segment EBITDA	(107)		(112)			(249)	(234)
Depreciation and amortization	$ 63		$ 56			$ 171	$ 150