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, 2022	Mar. 31, 2021
Revenues From Third Party Payers [Line Items]
Revenues	$ 14,945	$ 13,977
Revenues ratio from third party payers	100.00%	100.00%
Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,726	$ 2,559
Revenues from third party payers, Ratio	18.20%	18.30%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,324	$ 2,053
Revenues from third party payers, Ratio	15.60%	14.70%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 579	$ 527
Revenues from third party payers, Ratio	3.90%	3.80%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,110	$ 725
Revenues from third party payers, Ratio	7.40%	5.20%
Managed Care and Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 7,152	$ 6,885
Revenues from third party payers, Ratio	47.90%	49.10%
International (Managed Care and Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 356	$ 333
Revenues from third party payers, Ratio	2.40%	2.40%
Other [Member]
Revenues From Third Party Payers [Line Items]
Revenues	$ 698	$ 895
Other, Ratio	4.60%	6.50%