Acquisitions and Divestitures - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 28, 2018
Business Acquisition [Line Items]
Goodwill	$ 79,552	$ 79,749	$ 78,678
Aetna Inc.
Business Acquisition [Line Items]
Cash and cash equivalents				$ 6,565
Accounts receivable				4,094
Other current assets				3,894
Investments (current and long-term)				17,984
Goodwill				47,755
Intangible assets				22,571
Other assets				8,249
Total assets acquired				111,112
Health care costs payable				5,302
Other current liabilities				9,940
Debt (current and long-term)				8,098
Deferred income taxes				4,608
Other long-term liabilities				13,078
Total liabilities assumed				41,026
Noncontrolling interests				320
Total consideration transferred				$ 69,766