Segment Reporting (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Gross inpatient revenues										$ 40,281,027	$ 38,531,825	$ 34,550,480
Gross outpatient revenues										17,236,319	18,733,333	15,993,034
Total net revenues		$ 3,086,935	$ 2,912,541	$ 2,729,754	$ 2,829,667	$ 2,896,247	$ 2,822,453	$ 2,855,168	$ 2,804,391	11,558,897	11,378,259	10,772,278
Income (loss) before allocation of corporate overhead and income taxes										1,252,083	1,066,337	1,034,525
Allocation of corporate overhead										0	0	0
Income before income taxes										1,252,083	1,066,337	1,034,525
Total assets		13,476,879				11,668,250				13,476,879	11,668,250	11,265,480
Acute Care Hospital Services
Segment Reporting Information [Line Items]
Gross inpatient revenues										30,562,093	28,430,922	24,814,959
Gross outpatient revenues										16,272,520	17,666,629	14,967,313
Total net revenues										6,337,304	6,164,560	5,719,905
Income (loss) before allocation of corporate overhead and income taxes										693,427	713,410	708,680
Allocation of corporate overhead										(223,921)	(230,166)	(199,823)
Income before income taxes										469,506	483,244	508,857
Total assets		4,927,456				4,405,643				4,927,456	4,405,643	4,094,537
Behavioral Health Services
Segment Reporting Information [Line Items]
Gross inpatient revenues	[1]									9,718,934	10,100,903	9,735,521
Gross outpatient revenues	[1]									963,799	1,066,704	1,025,721
Total net revenues	[1]									5,208,722	5,210,063	5,038,874
Income (loss) before allocation of corporate overhead and income taxes	[1]									1,023,257	900,965	915,517
Allocation of corporate overhead	[1]									(170,849)	(166,571)	(161,282)
Income before income taxes	[1]									852,408	734,394	754,235
Total assets	[1]	7,044,617				6,910,790				7,044,617	6,910,790	6,786,369
Other
Segment Reporting Information [Line Items]
Total net revenues										12,871	3,636	13,499
Income (loss) before allocation of corporate overhead and income taxes										(464,601)	(548,038)	(589,672)
Allocation of corporate overhead										394,770	396,737	361,105
Income before income taxes										(69,831)	(151,301)	(228,567)
Total assets		$ 1,504,806				$ 351,817				$ 1,504,806	$ 351,817	$ 384,574

[1] Includes net revenues generated from our behavioral health care facilities located in the U.K. amounting to approximately $584 million in 2020, $554 million in 2019 and $505 million in 2018.  Total assets at our U.K. behavioral health care facilities were approximately $1.334 billion as of December 31, 2020, $1.270 billion as of December 31, 2019 and $1.224 billion as of December 31, 2018. In addition, included in our 2019 Behavioral Health Services operating segment Income (loss) before allocation of corporate overhead and income taxes is a pre-tax $98 million provision for asset impairment to reduce the carrying value of a tradename intangible asset and real property assets. Included in our 2018 Behavioral Health Services operating segment Income (loss) before allocation of corporate overhead and income taxes is a pre-tax $49 million provision for asset impairment to reduce the carrying value of a tradename intangible asset.