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				9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2012	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 9,856	$ 9,220			$ 29,429	$ 27,282
Equity in earnings of affiliates	(9)	(14)			(38)	(32)
Adjusted segment EBITDA	1,815	1,828			5,784	5,472
Depreciation and amortization	482	460			1,424	1,361
Interest expense	411	427			1,255	1,314
Losses (gains) on sales of facilities	2	12			(2)	(20)
Losses on retirement of debt					125	226
Legal claim costs	77		$ 78	$ 175	77	78
Income before income taxes	843	929			2,905	2,513
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,580	4,334			13,928	12,766
Equity in earnings of affiliates	(1)	(6)			(8)	(12)
Adjusted segment EBITDA	919	952			3,084	2,755
Depreciation and amortization	195	187			572	564
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,772	4,350			13,972	12,949
Equity in earnings of affiliates	(9)	(8)			(25)	(23)
Adjusted segment EBITDA	1,035	959			3,026	2,942
Depreciation and amortization	219	212			662	627
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	504	536			1,529	1,567
Equity in earnings of affiliates	1				(5)	3
Adjusted segment EBITDA	(139)	(83)			(326)	(225)
Depreciation and amortization	$ 68	$ 61			$ 190	$ 170