Schedule of Disaggregates Revenue by Major Source (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Net revenues		$ 2,754,496	$ 2,648,913	$ 2,681,353	$ 2,687,516	$ 2,642,787	$ 2,541,864	$ 2,612,356	$ 2,612,858	$ 10,772,278	$ 10,409,865	$ 9,766,210
Percentage of Net Revenue										100.00%	100.00%	100.00%
Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,875,875	$ 1,816,840	$ 1,729,093
Percentage of Net Revenue										17.00%	17.00%	18.00%
Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 929,390	$ 791,403	$ 679,778
Percentage of Net Revenue										9.00%	8.00%	7.00%
Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,183,618	$ 1,206,364	$ 1,180,160
Percentage of Net Revenue										11.00%	12.00%	12.00%
Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,530,005	$ 1,388,751	$ 1,237,398
Percentage of Net Revenue										14.00%	13.00%	13.00%
Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues										$ 3,489,870	$ 3,361,521	$ 3,253,029
Percentage of Net Revenue										32.00%	32.00%	33.00%
UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 504,721	$ 426,575	$ 241,098
Percentage of Net Revenue										5.00%	4.00%	2.00%
Other Patient Revenue and Adjustments, Net
Disaggregation Of Revenue [Line Items]
Net revenues										$ 650,987	$ 717,971	$ 741,222
Percentage of Net Revenue										6.00%	7.00%	8.00%
Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 607,812	$ 700,440	$ 704,432
Percentage of Net Revenue										6.00%	7.00%	7.00%
Acute Care Hospital Services
Disaggregation Of Revenue [Line Items]
Net revenues										$ 5,719,905	$ 5,484,683	$ 5,112,950
Percentage of Net Revenue										100.00%	100.00%	100.00%
Acute Care Hospital Services | Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,296,152	$ 1,223,150	$ 1,114,911
Percentage of Net Revenue										23.00%	22.00%	22.00%
Acute Care Hospital Services | Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 730,387	$ 630,083	$ 536,224
Percentage of Net Revenue										13.00%	11.00%	10.00%
Acute Care Hospital Services | Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 487,197	$ 482,820	$ 424,934
Percentage of Net Revenue										9.00%	9.00%	8.00%
Acute Care Hospital Services | Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 554,438	$ 511,844	$ 444,164
Percentage of Net Revenue										10.00%	9.00%	9.00%
Acute Care Hospital Services | Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues										$ 2,093,890	$ 1,949,435	$ 1,845,571
Percentage of Net Revenue										37.00%	36.00%	36.00%
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										$ 167,570	$ 219,056	$ 284,872
Percentage of Net Revenue										3.00%	4.00%	6.00%
Acute Care Hospital Services | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 390,271	$ 468,295	$ 462,274
Percentage of Net Revenue										7.00%	9.00%	9.00%
Behavioral Health Services
Disaggregation Of Revenue [Line Items]
Net revenues	[1]									$ 5,038,874	$ 4,906,719	$ 4,645,007
Percentage of Net Revenue										100.00%	100.00%	100.00%
Behavioral Health Services | Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 579,723	$ 593,690	$ 614,182
Percentage of Net Revenue										12.00%	12.00%	13.00%
Behavioral Health Services | Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues										$ 199,003	$ 161,320	$ 143,554
Percentage of Net Revenue										4.00%	3.00%	3.00%
Behavioral Health Services | Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 696,421	$ 723,544	$ 755,226
Percentage of Net Revenue										14.00%	15.00%	16.00%
Behavioral Health Services | Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues										$ 975,567	$ 876,907	$ 793,234
Percentage of Net Revenue										19.00%	18.00%	17.00%
Behavioral Health Services | Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues										$ 1,395,980	$ 1,412,086	$ 1,407,458
Percentage of Net Revenue										28.00%	29.00%	30.00%
Behavioral Health Services | UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 504,721	$ 426,575	$ 241,098
Percentage of Net Revenue										10.00%	9.00%	5.00%
Behavioral Health Services | Other Patient Revenue and Adjustments, Net
Disaggregation Of Revenue [Line Items]
Net revenues										$ 483,417	$ 498,915	$ 456,350
Percentage of Net Revenue										10.00%	10.00%	10.00%
Behavioral Health Services | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 204,042	$ 213,682	$ 233,905
Percentage of Net Revenue										4.00%	4.00%	5.00%
Other
Disaggregation Of Revenue [Line Items]
Net revenues										$ 13,499	$ 18,463	$ 8,253
Other | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues										$ 13,499	$ 18,463	$ 8,253

[1] Includes net revenues generated from our behavioral health care facilities located in the U.K. amounting to approximately $505 million in 2018, $429 million in 2017 and $241 million in 2016. Total assets at our U.K. behavioral health care facilities were approximately $1.224 billion as of December 31, 2018, $1.098 billion as of December 31, 2017 and $965 million as of December 31, 2016. In addition, 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.