Basis of Presentation and Significant Accounting Policies - Schedule of Revenues from Third Party Payers and Uninsured (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 9,299	$ 8,351	$ 27,503	$ 25,310
Uninsured	313	717	1,019	1,809
Other	366	343	1,097	959
Revenues before provision for doubtful accounts	9,978	9,411	29,619	28,078
Provision for doubtful accounts	(758)	(955)	(2,337)	(2,732)
Revenues	9,220	8,456	27,282	25,346
Revenues from third party payers, Ratio	100.80%	98.70%	100.70%	99.80%
Uninsured, Ratio	3.40%	8.50%	3.70%	7.10%
Other, Ratio	4.00%	4.10%	4.00%	3.80%
Revenues before provision for doubtful accounts, Ratio	108.20%	111.30%	108.40%	110.70%
Revenues before provision for doubtful accounts, Ratio	108.20%	111.30%	108.40%	110.70%
Provision for doubtful accounts, Ratio	(8.20%)	(11.30%)	(8.40%)	(10.70%)
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	2,120	1,847	6,285	5,961
Revenues from third party payers, Ratio	23.00%	21.80%	23.00%	23.50%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	901	794	2,706	2,441
Revenues from third party payers, Ratio	9.80%	9.40%	9.90%	9.60%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	372	401	1,404	1,098
Revenues from third party payers, Ratio	4.00%	4.70%	5.10%	4.30%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	510	386	1,383	1,165
Revenues from third party payers, Ratio	5.50%	4.60%	5.10%	4.60%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	5,073	4,636	14,742	13,777
Revenues from third party payers, Ratio	55.00%	54.80%	54.00%	54.40%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 323	$ 287	$ 983	$ 868
Revenues from third party payers, Ratio	3.50%	3.40%	3.60%	3.40%