Schedule of Disaggregates Revenue by Major Source (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
Disaggregation Of Revenue [Line Items]
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
Percentage of Net Revenue										100.00%	100.00%	100.00%
Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,690,591	$ 1,889,245	$ 1,875,875
Percentage of Net Revenue										15.00%	17.00%	17.00%
Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,104,930	$ 1,047,759	$ 929,390
Percentage of Net Revenue										10.00%	9.00%	9.00%
Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,202,632	$ 1,207,649	$ 1,183,618
Percentage of Net Revenue										10.00%	11.00%	11.00%
Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,715,439	$ 1,678,641	$ 1,530,005
Percentage of Net Revenue										15.00%	15.00%	14.00%
Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues										$ 3,426,937	$ 3,634,817	$ 3,489,870
Percentage of Net Revenue										30.00%	32.00%	32.00%
UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 584,000	$ 553,831	$ 504,721
Percentage of Net Revenue										5.00%	5.00%	5.00%
Other Patient Revenue and Adjustments, Net
Disaggregation Of Revenue [Line Items]
Net revenues										$ 745,344	$ 696,566	$ 650,987
Percentage of Net Revenue										6.00%	6.00%	6.00%
Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,089,024	$ 669,751	$ 607,812
Percentage of Net Revenue										9.00%	6.00%	6.00%
Acute Care Hospital Services
Disaggregation Of Revenue [Line Items]
Net revenues										$ 6,337,304	$ 6,164,560	$ 5,719,905
Percentage of Net Revenue										100.00%	100.00%	100.00%
Acute Care Hospital Services | Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,242,268	$ 1,336,200	$ 1,296,152
Percentage of Net Revenue										20.00%	22.00%	23.00%
Acute Care Hospital Services | Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 869,488	$ 827,216	$ 730,387
Percentage of Net Revenue										14.00%	13.00%	13.00%
Acute Care Hospital Services | Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 551,551	$ 519,508	$ 487,197
Percentage of Net Revenue										9.00%	8.00%	9.00%
Acute Care Hospital Services | Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 491,234	$ 560,029	$ 554,438
Percentage of Net Revenue										8.00%	9.00%	10.00%
Acute Care Hospital Services | Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues										$ 2,146,018	$ 2,271,002	$ 2,093,890
Percentage of Net Revenue										34.00%	37.00%	37.00%
Acute Care Hospital Services | UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 0	$ 0	$ 0
Percentage of Net Revenue										0.00%	0.00%	0.00%
Acute Care Hospital Services | Other Patient Revenue and Adjustments, Net
Disaggregation Of Revenue [Line Items]
Net revenues										$ 248,047	$ 191,422	$ 167,570
Percentage of Net Revenue										4.00%	3.00%	3.00%
Acute Care Hospital Services | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 788,698	$ 459,183	$ 390,271
Percentage of Net Revenue										12.00%	7.00%	7.00%
Behavioral Health Services
Disaggregation Of Revenue [Line Items]
Net revenues	[1]									$ 5,208,722	$ 5,210,063	$ 5,038,874
Percentage of Net Revenue										100.00%	100.00%	100.00%
Behavioral Health Services | Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 448,323	$ 553,045	$ 579,723
Percentage of Net Revenue										9.00%	11.00%	12.00%
Behavioral Health Services | Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 235,442	$ 220,543	$ 199,003
Percentage of Net Revenue										5.00%	4.00%	4.00%
Behavioral Health Services | Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 651,081	$ 688,141	$ 696,421
Percentage of Net Revenue										12.00%	13.00%	14.00%
Behavioral Health Services | Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,224,205	$ 1,118,612	$ 975,567
Percentage of Net Revenue										24.00%	21.00%	19.00%
Behavioral Health Services | Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,280,919	$ 1,363,815	$ 1,395,980
Percentage of Net Revenue										25.00%	26.00%	28.00%
Behavioral Health Services | UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 584,000	$ 553,831	$ 504,721
Percentage of Net Revenue										11.00%	11.00%	10.00%
Behavioral Health Services | Other Patient Revenue and Adjustments, Net
Disaggregation Of Revenue [Line Items]
Net revenues										$ 497,297	$ 505,144	$ 483,417
Percentage of Net Revenue										10.00%	10.00%	10.00%
Behavioral Health Services | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 287,455	$ 206,932	$ 204,042
Percentage of Net Revenue										6.00%	4.00%	4.00%
Other
Disaggregation Of Revenue [Line Items]
Net revenues										$ 12,871	$ 3,636	$ 13,499
Other | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 12,871	$ 3,636	$ 13,499

[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.