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
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 13,977	$ 12,861
Equity in earnings of affiliates	(21)	(7)
Adjusted segment EBITDA	3,052	2,200
Depreciation and amortization	697	674
Interest expense	384	428
Gains on sales of facilities	(2)	(7)
Losses on retirement of debt	0	295
Income before income taxes	1,973	810
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	7,056	6,474
Equity in earnings of affiliates	(7)	1
Adjusted segment EBITDA	1,705	1,215
Depreciation and amortization	323	306
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	6,291	5,744
Equity in earnings of affiliates	(12)	(9)
Adjusted segment EBITDA	1,501	1,115
Depreciation and amortization	293	287
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	630	643
Equity in earnings of affiliates	(2)	1
Adjusted segment EBITDA	(154)	(130)
Depreciation and amortization	$ 81	$ 81