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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 10,911	$ 10,402	$ 21,728	$ 20,815
Uninsured	519	225	744	414
Other	376	454	717	902
Revenues before provision for doubtful accounts	11,806	11,081	23,189	22,131
Provision for doubtful accounts	(1,073)	(762)	(1,833)	(1,552)
Revenues	$ 10,733	$ 10,319	$ 21,356	$ 20,579
Revenues from third party payers, Ratio	101.70%	100.70%	101.70%	101.20%
Uninsured, Ratio	4.80%	2.20%	3.50%	2.00%
Other, Ratio	3.50%	4.40%	3.40%	4.40%
Revenues before provision for doubtful accounts, Ratio	110.00%	107.30%	108.60%	107.60%
Provision for doubtful accounts, Ratio	(10.00%)	(7.30%)	(8.60%)	(7.60%)
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	$ 2,321	$ 2,217	$ 4,726	$ 4,483
Revenues from third party payers, Ratio	21.60%	21.50%	22.10%	21.80%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,187	$ 1,078	$ 2,390	$ 2,182
Revenues from third party payers, Ratio	11.10%	10.40%	11.20%	10.60%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 453	$ 416	$ 826	$ 843
Revenues from third party payers, Ratio	4.20%	4.00%	3.90%	4.10%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 575	$ 608	$ 1,216	$ 1,205
Revenues from third party payers, Ratio	5.40%	5.90%	5.70%	5.90%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 6,106	$ 5,759	$ 12,032	$ 11,461
Revenues from third party payers, Ratio	56.90%	55.80%	56.30%	55.70%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 269	$ 324	$ 538	$ 641
Revenues from third party payers, Ratio	2.50%	3.10%	2.50%	3.10%