Accounting Policies - Schedule of Revenues from Third Party Payers, Uninsured and Other Payers (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues From Third Party Payers [Line Items]
Revenues from third party payers	$ 13,523	$ 12,694	$ 12,602	$ 12,517	$ 12,274	$ 11,451	$ 11,529	$ 11,423	$ 51,336	$ 46,677	$ 43,614
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									$ 10,798	$ 9,831	$ 9,285
Revenues from third party payers, Ratio									21.00%	21.10%	21.30%
Managed Medicare [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 6,452	$ 5,497	$ 4,680
Revenues from third party payers, Ratio									12.60%	11.80%	10.70%
Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 1,572	$ 1,358	$ 1,316
Revenues from third party payers, Ratio									3.10%	2.90%	3.00%
Managed Medicaid [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 2,450	$ 2,403	$ 2,165
Revenues from third party payers, Ratio									4.80%	5.10%	5.00%
Managed Care and Other Insurers [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 26,544	$ 24,467	$ 23,342
Revenues from third party payers, Ratio									51.60%	52.40%	53.50%
International (Managed Care and Other Insurers) [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 1,162	$ 1,156	$ 1,097
Revenues from third party payers, Ratio									2.30%	2.50%	2.50%
Product and Service, Other [Member]
Revenues From Third Party Payers [Line Items]
Revenues from third party payers									$ 2,358	$ 1,965	$ 1,729
Other, Ratio									4.60%	4.20%	4.00%