Segment Reporting (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
Segment Reporting Information [Line Items]
Gross inpatient revenues										$ 34,550,480	$ 30,838,191	$ 27,060,212
Gross outpatient revenues										15,993,034	14,109,290	12,276,200
Total 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
Income (loss) before allocation of corporate overhead and income taxes										1,034,525	1,135,009	1,156,358
Allocation of corporate overhead										0	0	0
Income before income taxes										1,034,525	1,135,009	1,156,358
Total assets		11,265,480				10,761,828				11,265,480	10,761,828	10,317,802
Acute Care Hospital Services
Segment Reporting Information [Line Items]
Gross inpatient revenues										24,814,959	21,888,207	19,042,627
Gross outpatient revenues										14,967,313	13,115,881	11,374,098
Total net revenues										5,719,905	5,484,683	5,112,950
Income (loss) before allocation of corporate overhead and income taxes										708,680	641,857	557,472
Allocation of corporate overhead										(199,823)	(182,713)	(170,767)
Income before income taxes										508,857	459,144	386,705
Total assets		4,094,537				3,849,214				4,094,537	3,849,214	3,723,075
Behavioral Health Services
Segment Reporting Information [Line Items]
Gross inpatient revenues	[1]									9,735,521	8,949,984	8,017,585
Gross outpatient revenues	[1]									1,025,721	993,409	902,102
Total net revenues	[1]									5,038,874	4,906,719	4,645,007
Income (loss) before allocation of corporate overhead and income taxes	[1]									915,517	968,974	1,030,734
Allocation of corporate overhead	[1]									(161,282)	(158,735)	(154,843)
Income before income taxes	[1]									754,235	810,239	875,891
Total assets	[1]	6,786,369				6,648,818				6,786,369	6,648,818	6,440,195
Other
Segment Reporting Information [Line Items]
Total net revenues										13,499	18,463	8,253
Income (loss) before allocation of corporate overhead and income taxes										(589,672)	(475,822)	(431,848)
Allocation of corporate overhead										361,105	341,448	325,610
Income before income taxes										(228,567)	(134,374)	(106,238)
Total assets		$ 384,574				$ 263,796				$ 384,574	$ 263,796	$ 154,532

[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.