Description of Business and Accounting Policies - Accounts Receivable, Net and Other (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 16,677	$ 13,164
Allowance for doubtful accounts	495	348	$ 237
Additions to allowance for doubtful accounts	878	626	451
Deductions to allowance for doubtful accounts	731	515	$ 403
Customer receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	9,400	6,400
Vendor receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	3,200	2,600
Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, net and other	$ 710	$ 692