Segment and Geographic Information - Schedule of Geographic Distributions of Revenues, Equity in Earnings or Losses of Affiliates, Adjusted Segment EBITDA, Depreciation and Amortization (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Segment Reporting Information [Line Items]
Revenues	$ 18,605	$ 17,492	$ 36,926	$ 34,831
Salaries and benefits	8,138	7,685	16,135	15,392
Supplies	2,844	2,634	5,608	5,305
Other operating expenses	3,793	3,623	7,638	7,229
Equity in losses (earnings) of affiliates	(19)	0	(37)	2
Depreciation and amortization	863	819	1,723	1,614
Interest expense	568	506	1,115	1,018
Losses (gains) on sales of facilities	3	(12)	2	(213)
Income before income taxes	2,415	2,237	4,742	4,484
Assets	59,536		59,536		$ 59,513
Operating Segments [Member]
Segment Reporting Information [Line Items]
Adjusted segment EBITDA	4,201	3,805	8,213	7,429
Eliminations and Reconciling Items [Member]
Segment Reporting Information [Line Items]
Corporate and Other	352	255	631	526
Depreciation and amortization	863	819	1,723	1,614
Interest expense	568	506	1,115	1,018
Losses (gains) on sales of facilities	3	(12)	2	(213)
Income before income taxes	2,415	2,237	4,742	4,484
National Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	5,200	4,856	10,265	9,691
Salaries and benefits	1,919	1,869	3,878	3,759
Supplies	755	693	1,496	1,398
Other operating expenses	1,255	1,204	2,488	2,398
Equity in losses (earnings) of affiliates		3		2
Operating expenses	3,929	3,769	7,862	7,557
Adjusted segment EBITDA	1,271	1,087	2,403	2,134
Depreciation and amortization	223	211	449	423
Assets	13,139		13,139		12,855
Atlantic Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	6,122	5,881	12,289	11,691
Salaries and benefits	2,246	2,149	4,462	4,310
Supplies	935	884	1,849	1,793
Other operating expenses	1,590	1,544	3,166	3,026
Equity in losses (earnings) of affiliates	(1)	(1)	(2)	(2)
Operating expenses	4,770	4,576	9,475	9,127
Adjusted segment EBITDA	1,352	1,305	2,814	2,564
Depreciation and amortization	275	261	549	519
Assets	17,365		17,365		17,168
American Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	6,493	6,043	12,824	12,027
Salaries and benefits	2,216	2,110	4,412	4,229
Supplies	1,067	978	2,087	1,958
Other operating expenses	1,649	1,560	3,360	3,140
Equity in losses (earnings) of affiliates	(17)	(18)	(31)	(31)
Operating expenses	4,915	4,630	9,828	9,296
Adjusted segment EBITDA	1,578	1,413	2,996	2,731
Depreciation and amortization	277	267	556	522
Assets	20,900		20,900		20,714
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenues	790	712	1,548	1,422
Depreciation and amortization	88	$ 80	169	$ 150
Assets	$ 8,132		$ 8,132		$ 8,776