Accounting Policies - Schedule of Revenues from Third Party Payers, Uninsured and Other Payers (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 41,961	$ 39,903	$ 37,116
Uninsured									1,135	1,927	1,494
Other									1,651	1,761	1,477
Revenues before provision for doubtful accounts									44,747	43,591	40,087
Provision for doubtful accounts									(3,257)	(3,913)	(3,169)
Revenues	$ 10,641	$ 10,270	$ 10,319	$ 10,260	$ 10,249	$ 9,856	$ 9,897	$ 9,676	$ 41,490	$ 39,678	$ 36,918
Revenues from third party payers, Ratio									101.10%	100.60%	100.60%
Uninsured, Ratio									2.70%	4.90%	4.00%
Other, Ratio									4.00%	4.40%	4.00%
Revenues before provision for doubtful accounts, Ratio									107.80%	109.90%	108.60%
Provision for doubtful accounts, Ratio									(7.80%)	(9.90%)	(8.60%)
Revenues ratio from third party payers									100.00%	100.00%	100.00%
Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 8,895	$ 8,654	$ 8,354
Revenues from third party payers, Ratio									21.40%	21.80%	22.60%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 4,355	$ 4,133	$ 3,614
Revenues from third party payers, Ratio									10.50%	10.40%	9.80%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 1,597	$ 1,705	$ 1,848
Revenues from third party payers, Ratio									3.80%	4.30%	5.00%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 2,478	$ 2,234	$ 1,923
Revenues from third party payers, Ratio									6.00%	5.60%	5.20%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 23,441	$ 21,882	$ 20,066
Revenues from third party payers, Ratio									56.50%	55.20%	54.40%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 1,195	$ 1,295	$ 1,311
Revenues from third party payers, Ratio									2.90%	3.30%	3.60%