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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 10,733	$ 10,319	$ 21,356	$ 20,579
Equity in earnings of affiliates	13	10	23	22
Adjusted segment EBITDA	2,090	2,052	4,095	4,055
Depreciation and amortization	521	489	1,042	968
Interest expense	411	427	830	843
Gains on sales of facilities	(2)	(6)	(3)	(5)
Legal claim costs		10		22
Income before income taxes	1,160	1,132	2,226	2,227
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,160	4,931	10,308	9,898
Equity in earnings of affiliates	(4)	(2)	(9)	(4)
Adjusted segment EBITDA	1,162	1,131	2,293	2,269
Depreciation and amortization	217	201	431	398
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,093	4,860	10,088	9,646
Equity in earnings of affiliates	(10)	(8)	(18)	(17)
Adjusted segment EBITDA	1,040	1,004	2,047	1,986
Depreciation and amortization	238	225	476	444
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	480	528	960	1,035
Equity in earnings of affiliates	1		4	(1)
Adjusted segment EBITDA	(112)	(83)	(245)	(200)
Depreciation and amortization	$ 66	$ 63	$ 135	$ 126