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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenues From Third Party Payers [Line Items]
Revenues	$ 14,820	$ 14,435	$ 29,765	$ 28,412
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	$ 2,495	$ 2,612	$ 5,221	$ 5,171
Revenues from third party payers, Ratio	16.80%	18.10%	17.50%	18.20%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,260	$ 2,104	$ 4,584	$ 4,157
Revenues from third party payers, Ratio	15.20%	14.60%	15.40%	14.60%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 611	$ 503	$ 1,190	$ 1,030
Revenues from third party payers, Ratio	4.10%	3.50%	4.00%	3.60%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 954	$ 831	$ 2,064	$ 1,556
Revenues from third party payers, Ratio	6.40%	5.80%	6.90%	5.50%
Managed Care and Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 7,144	$ 7,417	$ 14,296	$ 14,302
Revenues from third party payers, Ratio	48.40%	51.30%	48.10%	50.40%
International (Managed Care and Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 325	$ 338	$ 681	$ 671
Revenues from third party payers, Ratio	2.20%	2.30%	2.30%	2.40%
Other [Member]
Revenues From Third Party Payers [Line Items]
Revenues	$ 1,031	$ 630	$ 1,729	$ 1,525
Other, Ratio	6.90%	4.40%	5.80%	5.30%