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
	Dec. 09, 2015	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2014	Dec. 31, 2012	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues		$ 10,270	$ 9,856			$ 30,849	$ 29,429
Equity in earnings of affiliates		22	9			44	38
Adjusted segment EBITDA		1,957	1,815			6,012	5,784
Depreciation and amortization		495	482			1,463	1,424
Interest expense		432	411			1,275	1,255
Losses (gains) on sales of facilities		(3)	2			(8)	(2)
Losses on retirement of debt		4				4	125
Legal claim costs	$ 434	11	77	$ 78	$ 175	33	77
Income before income taxes		1,018	843			3,245	2,905
National Group [Member]
Segment Reporting Information [Line Items]
Revenues		4,882	4,580			14,780	13,928
Equity in earnings of affiliates		(13)	(1)			(17)	(8)
Adjusted segment EBITDA		1,073	920			3,342	3,089
Depreciation and amortization		204	195			602	572
American Group [Member]
Segment Reporting Information [Line Items]
Revenues		4,904	4,772			14,539	13,972
Equity in earnings of affiliates		(9)	(9)			(26)	(25)
Adjusted segment EBITDA		1,018	1,036			3,005	3,029
Depreciation and amortization		230	219			673	662
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues		484	504			1,530	1,529
Equity in earnings of affiliates			1			(1)	(5)
Adjusted segment EBITDA		(134)	(141)			(335)	(334)
Depreciation and amortization		$ 61	$ 68			$ 188	$ 190