Accounting Policies and Supplemental Disclosures - Accounts Receivable, Net and Other (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 28,610	$ 24,542
Allowance for doubtful accounts	951	1,100
Customer receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	17,700	14,800
Vendor receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	4,000	4,800
Seller receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 858	$ 381