Basis of Presentation and Significant Accounting Policies - Schedule of Estimated Cost of Uncompensated Care (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Patient care costs (salaries and benefits, supplies, other operating expenses and depreciation and amortization)	$ 9,871	$ 9,177	$ 19,738	$ 18,326
Cost-to-charges ratio (patient care costs as percentage of gross patient charges)	12.60%	13.00%	12.50%	12.90%
Total uncompensated care	$ 6,486	$ 5,721	$ 12,738	$ 11,048
Multiply by the cost-to-charges ratio	12.60%	13.00%	12.50%	12.90%
Estimated cost of total uncompensated care	$ 817	$ 743	$ 1,592	$ 1,425