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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 13,311	$ 12,694	$ 37,240	$ 37,813
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	$ 2,603	$ 2,592	$ 7,618	$ 7,997
Revenues from third party payers, Ratio	19.60%	20.40%	20.50%	21.20%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,760	$ 1,615	$ 5,074	$ 4,799
Revenues from third party payers, Ratio	13.20%	12.70%	13.60%	12.70%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 445	$ 361	$ 1,423	$ 1,124
Revenues from third party payers, Ratio	3.30%	2.80%	3.80%	3.00%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 707	$ 641	$ 1,904	$ 1,808
Revenues from third party payers, Ratio	5.30%	5.00%	5.10%	4.80%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 6,752	$ 6,554	$ 19,028	$ 19,405
Revenues from third party payers, Ratio	50.70%	51.70%	51.00%	51.10%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 307	$ 282	$ 838	$ 863
Revenues from third party payers, Ratio	2.30%	2.20%	2.30%	2.30%
Product and Service, Other [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 737	$ 649	$ 1,355	$ 1,817
Other, Ratio	5.60%	5.20%	3.70%	4.90%