Basis of Presentation and Significant Accounting Policies - Schedule of Estimated Cost of Uncompensated Care (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Patient care costs (salaries and benefits, supplies, other operating expenses and depreciation and amortization)	$ 11,170	$ 11,060	$ 32,428	$ 32,619
Cost-to-charges ratio (patient care costs as percentage of gross patient charges)	12.00%	12.30%	12.10%	12.10%
Total uncompensated care	$ 7,023	$ 7,923	$ 21,625	$ 22,703
Multiply by the cost-to-charges ratio	12.00%	12.30%	12.10%	12.10%
Estimated cost of total uncompensated care	$ 843	$ 975	$ 2,617	$ 2,747