Basis of Presentation and Significant Accounting Policies - Schedule of Estimated Cost of Uncompensated Care (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Accounting Policies [Abstract]
Patient care costs (salaries and benefits, supplies, other operating expenses and depreciation and amortization)	$ 10,606	$ 9,867
Cost-to-charges ratio (patient care costs as percentage of gross patient charges)	11.80%	12.40%
Total uncompensated care	$ 7,085	$ 6,252
Multiply by the cost-to-charges ratio	11.80%	12.40%
Estimated cost of total uncompensated care	$ 836	$ 775

$ 10,606

$ 9,867

$ 7,085

$ 6,252

$ 836

$ 775