Description of Business, Accounting Policies, and Supplemental Disclosures - Accounts Receivable, Net and Other (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 24,542	$ 20,816
Allowance for doubtful accounts	1,100	718	$ 495
Additions to allowance for doubtful accounts	1,400	1,000	878
Deductions to allowance for doubtful accounts	1,000	793	$ 731
Customer receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	14,800	12,600
Vendor receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	4,800	4,200
Seller receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 381	$ 863