Commitments and Contingencies - Additional Information (Detail) £ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2023 GBP (£)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2023 GBP (£)	Jun. 01, 2023 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2014 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability, current	$ 55,000,000		$ 55,000,000		$ 74,000,000
Compensation liability claims	127,000,000		127,000,000		125,000,000
Pre-tax decrease to reserves for self-insured workers' compensation liability claims		$ 10,000,000
Compensation and related benefits	55,000,000		55,000,000		55,000,000
District Facilities
Commitments and Contingencies Disclosure [Line Items]
Projected aggregate development and construction cost	439,000,000		439,000,000
Development and construction cost incurred	$ 152,000,000		$ 152,000,000
Lease initial terms	75 years		75 years							75 years
Committment to expend			$ 75,000,000
Projected commitment expend period			12 years	12 years
Department of Human Services
Commitments and Contingencies Disclosure [Line Items]
Repayment of legal settlement amount on demand			$ 4,000,000
Amount claimed from over payments of legal settlements			4,000,000				$ 7,000,000	$ 8,000,000	$ 7,000,000
Amount claimed from over payments of legal settlements due to change in calculations							$ 3,000,000	$ 2,000,000	$ 2,000,000
Wind Storms
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	$ 250,000,000		250,000,000
Maximum insurance deductible											$ 5,000,000
Cygnet Health Care Limited
Commitments and Contingencies Disclosure [Line Items]
Property insurance | £				£ 1,500
Maximum
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	$ 1,000,000,000		$ 1,000,000,000
Lease initial terms	10 years		10 years							10 years
Maximum | Wind Storms
Commitments and Contingencies Disclosure [Line Items]
Percentage of insurance deductible	5.00%		5.00%							5.00%
Maximum | Earthquake | CALIFORNIA
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	$ 100,000,000		$ 100,000,000
Maximum | Earthquake | Faulty Zones of UNITED STATES
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	100,000,000		100,000,000
Maximum | Earthquake | PUERTO RICO
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	40,000,000		40,000,000
Maximum | Earthquake | OTHER STATES
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	250,000,000		250,000,000
Maximum | Flood
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	100,000,000		100,000,000
Maximum | Flood | PUERTO RICO
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	1,000,000		1,000,000
Maximum | Flood | Texas
Commitments and Contingencies Disclosure [Line Items]
Commercial property insurance policies	$ 10,000,000		$ 10,000,000
Minimum
Commitments and Contingencies Disclosure [Line Items]
Lease initial terms	5 years		5 years							5 years
Minimum | Wind Storms
Commitments and Contingencies Disclosure [Line Items]
Percentage of insurance deductible	3.00%		3.00%							3.00%
General And Professional Liability Insurance Policies
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability	$ 5,000,000	$ 20,000,000	$ 25,000,000		16,000,000	$ 52,000,000
General and Professional Liability
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability	429,000,000		429,000,000		$ 372,000,000
Subsidiaries | Professional Liability | Cygnet Health Care Limited
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability | £										£ 16
Subsidiaries | Professional Liability | Maximum
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability	20,000,000		20,000,000											$ 10,000,000	$ 5,000,000	$ 10,000,000
Subsidiaries | General Liability | Cygnet Health Care Limited
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability | £										£ 25
Subsidiaries | General Liability | Maximum
Commitments and Contingencies Disclosure [Line Items]
Self-insured for professional and general liability	3,000,000		3,000,000											$ 3,000,000	$ 3,000,000	$ 3,000,000
Subsidiaries | General And Professional Liability Insurance Policies | Maximum
Commitments and Contingencies Disclosure [Line Items]
Purchased several excess policies through commercial insurance carriers per occurrence	$ 165,000,000		$ 165,000,000									$ 162,000,000	$ 155,000,000				$ 250,000,000