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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 13,311	$ 12,694	$ 37,240	$ 37,813
Equity in earnings of affiliates	(40)	(4)	(48)	(23)
Adjusted segment EBITDA	2,053	2,285	6,919	7,119
Depreciation and amortization	694	647	2,059	1,902
Interest expense	385	448	1,201	1,386
Losses (gains) on sales of facilities	(14)	0	6	(17)
Losses on retirement of debt	0	211	295	211
Income before income taxes	988	979	3,358	3,637
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	6,633	6,398	18,653	19,159
Equity in earnings of affiliates	(23)	2	(26)	(3)
Adjusted segment EBITDA	1,128	1,270	3,828	4,088
Depreciation and amortization	312	291	930	839
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	6,073	5,780	16,920	17,001
Equity in earnings of affiliates	(15)	(10)	(26)	(32)
Adjusted segment EBITDA	1,130	1,185	3,653	3,443
Depreciation and amortization	286	277	868	828
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	605	516	1,667	1,653
Equity in earnings of affiliates	(2)	4	4	12
Adjusted segment EBITDA	(205)	(170)	(562)	(412)
Depreciation and amortization	$ 96	$ 79	$ 261	$ 235