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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 15,276	$ 13,311		$ 43,688	$ 37,240
Equity in earnings of affiliates	(35)	(40)		(78)	(48)
Adjusted segment EBITDA	3,224	2,053		9,495	6,919
Depreciation and amortization	716	694		2,125	2,059
Interest expense	398	385		1,168	1,201
Losses (gains) on sales of facilities	(1,047)	(14)		(1,057)	6
Losses on retirement of debt	0	0	$ 12	12	295
Income before income taxes	3,157	988		7,247	3,358
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	7,787	6,633		22,143	18,653
Equity in earnings of affiliates	(14)	(23)		(30)	(26)
Adjusted segment EBITDA	1,780	1,128		5,330	3,828
Depreciation and amortization	343	312		1,005	930
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	6,767	6,073		19,562	16,920
Equity in earnings of affiliates	(14)	(15)		(38)	(26)
Adjusted segment EBITDA	1,604	1,130		4,698	3,653
Depreciation and amortization	295	286		884	868
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	722	605		1,983	1,667
Equity in earnings of affiliates	(7)	(2)		(10)	4
Adjusted segment EBITDA	(160)	(205)		(533)	(562)
Depreciation and amortization	$ 78	$ 96		$ 236	$ 261