Accounting Policies - Accounts Receivable, Net and Other (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 17,836	$ 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	11,300	12,600
Vendor Receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	2,700	4,200
Seller Receivables, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 801	$ 863