Acquisitions and Divestitures - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) Facility Bed
2020 Divestiture of Assets and Businesses
Business Acquisition [Line Items]
Aggregate cash proceeds from divestiture of businesses	$ 8
2019 Divestiture of Assets
Business Acquisition [Line Items]
Aggregate cash proceeds from divestiture of businesses		$ 9
Located in U.K. | 2018 Divestiture of Assets and Businesses
Business Acquisition [Line Items]
Aggregate cash proceeds from divestiture of businesses			$ 13
Number of beds | Bed			18
2020 Acquisitions of Assets and Businesses | Nevada
Business Acquisition [Line Items]
Acquisition, cash paid	$ 52
2019 Acquisitions of Assets and Businesses
Business Acquisition [Line Items]
Acquisition, cash paid		$ 8
2018 Acquisitions of Assets and Businesses
Business Acquisition [Line Items]
Acquisition, cash paid			$ 110
Goodwill recognition description	Goodwill of the facilities acquired during each of the last 3 years is computed, pursuant to the residual method, by deducting the fair value of the acquired assets and liabilities from the total purchase price. The factors that contribute to the recognition of goodwill, which may also influence the purchase price, include the following for each of the acquired facilities: (i) the historical cash flows and income levels; (ii) the reputations in their respective markets; (iii) the nature of the respective operations, and; (iv) the future cash flows and income growth projections.
Danshell Group [Member] | Located in U.K.
Business Acquisition [Line Items]
Number of behavioral health care facilities | Facility			25
Gulfport Behavioral Health System | Located in Gulfport
Business Acquisition [Line Items]
Number of beds | Bed			109