Basis of Presentation and Significant Accounting Policies - Schedule of Revenues from Third Party Payers, Uninsured and Other Payers (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 10,413	$ 9,824
Uninsured	189	68
Other	448	430
Revenues before provision for doubtful accounts	11,050	10,322
Provision for doubtful accounts	(790)	(646)
Revenues	$ 10,260	$ 9,676
Revenues from third party payers, Ratio	101.60%	101.60%
Uninsured, Ratio	1.80%	0.70%
Other, Ratio	4.40%	4.40%
Revenues before provision for doubtful accounts, Ratio	107.80%	106.70%
Provision for doubtful accounts, Ratio	(7.80%)	(6.70%)
Revenues ratio from third party payers	100.00%	100.00%
Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,266	$ 2,234
Revenues from third party payers, Ratio	22.10%	23.10%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,104	$ 1,052
Revenues from third party payers, Ratio	10.80%	10.90%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 427	$ 452
Revenues from third party payers, Ratio	4.20%	4.70%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 597	$ 549
Revenues from third party payers, Ratio	5.80%	5.70%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 5,702	$ 5,216
Revenues from third party payers, Ratio	55.60%	53.90%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 317	$ 321
Revenues from third party payers, Ratio	3.10%	3.30%