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	3 Months Ended				6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2012	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 9,897	$ 9,230			$ 19,573	$ 18,062
Equity in earnings of affiliates	(10)	(9)			(29)	(18)
Adjusted segment EBITDA	2,008	2,000			3,969	3,644
Depreciation and amortization	469	454			942	901
Interest expense	425	427			844	887
Losses (gains) on sales of facilities	5	(11)			(4)	(32)
Losses on retirement of debt	125	226			125	226
Legal claim costs			$ 78	$ 175		78
Income before income taxes	984	904			2,062	1,584
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,698	4,270			9,348	8,432
Equity in earnings of affiliates	(4)	(3)			(7)	(6)
Adjusted segment EBITDA	1,086	946			2,165	1,803
Depreciation and amortization	188	190			377	377
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,699	4,447			9,200	8,599
Equity in earnings of affiliates	(8)	(8)			(16)	(15)
Adjusted segment EBITDA	1,043	1,133			1,991	1,983
Depreciation and amortization	222	210			443	415
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	500	513			1,025	1,031
Equity in earnings of affiliates	2	2			(6)	3
Adjusted segment EBITDA	(121)	(79)			(187)	(142)
Depreciation and amortization	$ 59	$ 54			$ 122	$ 109