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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 10,390	$ 9,881	$ 31,205	$ 29,632
Uninsured	336	695	750	1,321
Other	384	438	1,286	1,315
Revenues before provision for doubtful accounts	11,110	11,014	33,241	32,268
Provision for doubtful accounts	(840)	(1,158)	(2,392)	(2,839)
Revenues	$ 10,270	$ 9,856	$ 30,849	$ 29,429
Revenues from third party payers, Ratio	101.20%	100.30%	101.10%	100.70%
Uninsured, Ratio	3.30%	7.00%	2.40%	4.50%
Other, Ratio	3.70%	4.40%	4.20%	4.50%
Revenues before provision for doubtful accounts, Ratio	108.20%	111.70%	107.70%	109.70%
Provision for doubtful accounts, Ratio	(8.20%)	(11.70%)	(7.70%)	(9.70%)
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	$ 2,158	$ 2,122	$ 6,641	$ 6,500
Revenues from third party payers, Ratio	21.00%	21.50%	21.50%	22.10%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,068	$ 1,031	$ 3,250	$ 3,099
Revenues from third party payers, Ratio	10.40%	10.50%	10.50%	10.50%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 405	$ 402	$ 1,248	$ 1,262
Revenues from third party payers, Ratio	3.90%	4.10%	4.00%	4.30%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 611	$ 553	$ 1,816	$ 1,673
Revenues from third party payers, Ratio	6.00%	5.60%	5.90%	5.70%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 5,863	$ 5,457	$ 17,324	$ 16,134
Revenues from third party payers, Ratio	57.10%	55.40%	56.20%	54.80%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 285	$ 316	$ 926	$ 964
Revenues from third party payers, Ratio	2.80%	3.20%	3.00%	3.30%