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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 9,927	$ 9,279	$ 19,751	$ 18,204
Uninsured	558	318	626	706
Other	447	361	877	731
Revenues before provision for doubtful accounts	10,932	9,958	21,254	19,641
Provision for doubtful accounts	(1,035)	(728)	(1,681)	(1,579)
Revenues	$ 9,897	$ 9,230	$ 19,573	$ 18,062
Revenues from third party payers, Ratio	100.30%	100.60%	100.90%	100.80%
Uninsured, Ratio	5.60%	3.40%	3.20%	3.90%
Other, Ratio	4.50%	3.90%	4.50%	4.00%
Revenues before provision for doubtful accounts, Ratio	110.40%	107.90%	108.60%	108.70%
Provision for doubtful accounts, Ratio	(10.40%)	(7.90%)	(8.60%)	(8.70%)
Revenues ratio from third party payers	100.00%	100.00%	100.00%	100.00%
Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,144	$ 2,040	$ 4,378	$ 4,165
Revenues from third party payers, Ratio	21.70%	22.10%	22.40%	23.10%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,016	$ 906	$ 2,068	$ 1,805
Revenues from third party payers, Ratio	10.30%	9.80%	10.60%	10.00%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 408	$ 588	$ 860	$ 1,032
Revenues from third party payers, Ratio	4.10%	6.40%	4.40%	5.70%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 571	$ 452	$ 1,120	$ 873
Revenues from third party payers, Ratio	5.80%	4.90%	5.70%	4.80%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 5,461	$ 4,959	$ 10,677	$ 9,669
Revenues from third party payers, Ratio	55.10%	53.80%	54.50%	53.50%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 327	$ 334	$ 648	$ 660
Revenues from third party payers, Ratio	3.30%	3.60%	3.30%	3.70%