Accounting Policies - Schedule of Revenue Deductions Related to Uninsured Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Abstract]
Charity care	$ 4,151	$ 3,682	$ 3,775
Uninsured discounts	13,047	10,692	8,999
Provision for doubtful accounts	3,257	3,913	3,169
Total uncompensated care	$ 20,455	$ 18,287	$ 15,943
Charity care, ratio	20.00%	20.00%	24.00%
Uninsured discounts, ratio	64.00%	59.00%	56.00%
Provision for doubtful accounts, ratio	16.00%	21.00%	20.00%
Total uncompensated care, ratio	100.00%	100.00%	100.00%