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
	Mar. 31, 2020	Mar. 31, 2019
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 12,861	$ 12,517
Revenues ratio from third party payers	100.00%	100.00%
Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,743	$ 2,770
Revenues from third party payers, Ratio	21.30%	22.10%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,826	$ 1,589
Revenues from third party payers, Ratio	14.20%	12.70%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 414	$ 347
Revenues from third party payers, Ratio	3.20%	2.80%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 666	$ 613
Revenues from third party payers, Ratio	5.20%	4.90%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 6,645	$ 6,426
Revenues from third party payers, Ratio	51.60%	51.40%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 292	$ 297
Revenues from third party payers, Ratio	2.30%	2.40%
Product and Service, Other [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 275	$ 475
Other, Ratio	2.20%	3.70%