Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2017	Nov. 30, 2017	Sep. 30, 2018 USD ($) State Hospital Surgery_Center	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) State Hospital Surgery_Center	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of owned and operated hospitals | Hospital			179		179
Number of freestanding surgery centers | Surgery_Center			122		122
Number of facilities locations | State			20		20
General and administrative expense			$ 90	$ 83	$ 254	$ 247
Estimated implicit price concessions recorded as reductions to revenues and accounts receivable					$ 5,781		$ 5,488
Percentage of sum of revenues and uncompensated care			37.20%	36.30%	36.20%	34.80%
Charity care amount			$ 2,314	$ 1,235	$ 6,170	$ 3,494
Estimated costs of charity care			$ 295	$ 167	$ 777	$ 458
Inpatient Services [Member]
Summary Of Significant Accounting Policies [Line Items]
Performance obligations for inpatient/ outpatient services satisfied period			5 days		5 days
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of income of federal poverty level eligible for charity care	200.00%	400.00%
Maximum [Member] | Outpatient Services [Member]
Summary Of Significant Accounting Policies [Line Items]
Performance obligations for inpatient/ outpatient services satisfied period			1 day		1 day
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of income of federal poverty level eligible for charity care		200.00%