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	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 58,752	$ 51,533	$ 51,336
Equity in earnings of affiliates	(113)	(54)	(43)
Adjusted segment EBITDA	12,644	10,037	9,857
Depreciation and amortization	2,853	2,721	2,596
Interest expense	1,566	1,584	1,824
Losses (gains) on sales of facilities	(1,620)	7	(18)
Losses on retirement of debt	12	295	211
Income before income taxes	9,833	5,430	5,244
Assets	50,742	47,490	45,058
Goodwill and other intangible assets, Beginning Balance	8,578	8,269	7,953
Goodwill and other intangible assets, Acquisitions	1,062	344	332
Goodwill and other intangible assets, Foreign currency translation, amortization and other	(100)	(35)	(16)
Goodwill and other intangible assets, Ending Balance	9,540	8,578	8,269
National Group [Member]
Segment Reporting Information [Line Items]
Revenues	29,826	25,694	25,913
Equity in earnings of affiliates	(33)	(28)	(2)
Adjusted segment EBITDA	7,200	5,532	5,634
Depreciation and amortization	1,359	1,216	1,161
Assets	21,205	18,913	18,290
Goodwill and other intangible assets, Beginning Balance	1,775	1,739	1,597
Goodwill and other intangible assets, Acquisitions	735	38	155
Goodwill and other intangible assets, Foreign currency translation, amortization and other	(18)	(2)	(13)
Goodwill and other intangible assets, Ending Balance	2,492	1,775	1,739
American Group [Member]
Segment Reporting Information [Line Items]
Revenues	26,152	23,593	23,173
Equity in earnings of affiliates	(53)	(42)	(44)
Adjusted segment EBITDA	6,156	5,333	4,904
Depreciation and amortization	1,183	1,164	1,117
Assets	21,428	20,760	20,608
Goodwill and other intangible assets, Beginning Balance	5,775	5,765	5,729
Goodwill and other intangible assets, Acquisitions	67	27	39
Goodwill and other intangible assets, Foreign currency translation, amortization and other	(10)	(17)	(3)
Goodwill and other intangible assets, Ending Balance	5,832	5,775	5,765
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	2,774	2,246	2,250
Equity in earnings of affiliates	(27)	16	3
Adjusted segment EBITDA	(712)	(828)	(681)
Depreciation and amortization	311	341	318
Assets	8,109	7,817	6,160
Goodwill and other intangible assets, Beginning Balance	1,028	765	627
Goodwill and other intangible assets, Acquisitions	260	279	138
Goodwill and other intangible assets, Foreign currency translation, amortization and other	(72)	(16)
Goodwill and other intangible assets, Ending Balance	$ 1,216	$ 1,028	$ 765