Description of Business and Accounting Policies - Accounts Receivable, Net and Other (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 20,816	$ 16,677
Allowance for doubtful accounts	718	495	$ 348
Additions to allowance for doubtful accounts	1,000	878	626
Deductions to allowance for doubtful accounts	793	731	$ 515
Customer receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	12,600	9,400
Vendor receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	4,200	3,200
Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 863	$ 710