Accounting Policies and Supplemental Disclosures - Accounts Receivable, Net and Other (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 19,918	$ 20,816
Accounts Receivable, Allowance for Credit Loss, Current	1,100	718
Customer Receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	12,200	12,600
Vendor Receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	3,100	4,200
Seller Receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 543	$ 863