Accounting Policies - Schedule of Estimated Cost of Uncompensated Care (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Patient care costs (salaries and benefits, supplies, other operating expenses and depreciation and amortization)	$ 37,557	$ 35,304	$ 33,760
Cost-to-charges ratio (patient care costs as percentage of gross patient charges)	12.90%	13.50%	14.50%
Total uncompensated care	$ 23,420	$ 20,455	$ 18,287
Multiply by the cost-to-charges ratio	12.90%	13.50%	14.50%
Estimated cost of total uncompensated care	$ 3,021	$ 2,761	$ 2,652