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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 9,881	$ 9,299	$ 29,632	$ 27,503
Uninsured	695	313	1,321	1,019
Other	438	366	1,315	1,097
Revenues before provision for doubtful accounts	11,014	9,978	32,268	29,619
Provision for doubtful accounts	(1,158)	(758)	(2,839)	(2,337)
Revenues	$ 9,856	$ 9,220	$ 29,429	$ 27,282
Revenues from third party payers, Ratio	100.30%	100.80%	100.70%	100.70%
Uninsured, Ratio	7.00%	3.40%	4.50%	3.70%
Other, Ratio	4.40%	4.00%	4.50%	4.00%
Revenues before provision for doubtful accounts, Ratio	111.70%	108.20%	109.70%	108.40%
Provision for doubtful accounts, Ratio	(11.70%)	(8.20%)	(9.70%)	(8.40%)
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	$ 2,122	$ 2,120	$ 6,500	$ 6,285
Revenues from third party payers, Ratio	21.50%	23.00%	22.10%	23.00%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,031	$ 901	$ 3,099	$ 2,706
Revenues from third party payers, Ratio	10.50%	9.80%	10.50%	9.90%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 402	$ 372	$ 1,262	$ 1,404
Revenues from third party payers, Ratio	4.10%	4.00%	4.30%	5.10%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 553	$ 510	$ 1,673	$ 1,383
Revenues from third party payers, Ratio	5.60%	5.50%	5.70%	5.10%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 5,457	$ 5,073	$ 16,134	$ 14,742
Revenues from third party payers, Ratio	55.40%	55.00%	54.80%	54.00%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 316	$ 323	$ 964	$ 983
Revenues from third party payers, Ratio	3.20%	3.50%	3.30%	3.60%