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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Patient care costs (salaries and benefits, supplies, other operating expenses and depreciation and amortization)	$ 12,803	$ 11,170	$ 36,396	$ 32,428
Cost-to-charges ratio (patient care costs as percentage of gross patient charges)	11.80%	12.00%	11.40%	12.10%
Total uncompensated care	$ 7,782	$ 7,023	$ 22,299	$ 21,625
Multiply by the cost-to-charges ratio	11.80%	12.00%	11.40%	12.10%
Estimated cost of total uncompensated care	$ 916	$ 843	$ 2,542	$ 2,617