Accounting Policies - Schedule of Revenues from Third Party Payers, Uninsured and Other Payers (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 58,752	$ 51,533	$ 51,336
Revenues ratio from third party payers	100.00%	100.00%	100.00%
Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 10,447	$ 10,420	$ 10,798
Revenues from third party payers, Ratio	17.80%	20.20%	21.00%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 8,424	$ 6,997	$ 6,452
Revenues from third party payers, Ratio	14.30%	13.60%	12.60%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,290	$ 1,965	$ 1,572
Revenues from third party payers, Ratio	3.90%	3.80%	3.10%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 3,124	$ 2,621	$ 2,450
Revenues from third party payers, Ratio	5.30%	5.10%	4.80%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 30,295	$ 26,535	$ 26,544
Revenues from third party payers, Ratio	51.60%	51.50%	51.60%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 1,336	$ 1,120	$ 1,162
Revenues from third party payers, Ratio	2.30%	2.20%	2.30%
Product and Service, Other [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 2,836	$ 1,875	$ 2,358
Other, Ratio	4.80%	3.60%	4.60%