Current Receivables - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current receivables, gross	$ 6,296	$ 6,345
Less: Allowance for doubtful accounts	(327)	(330)
Total current receivables, net	5,969	6,015
Customer receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current receivables, gross	4,974	4,700
Related parties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current receivables, gross	653	801
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total current receivables, gross	$ 669	$ 844