Accounting Policies - Schedule of Changes in Accounting Policy (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts Receivable, net	$ 2,670	$ 2,028	$ 2,025
Prepaid Expenses and Other Current Assets	249	231	224
Deferred Income Taxes	1,908	2,009	2,008
Accounts Payable — Trade	2,819	2,814	2,807
Other Current Liabilities	795	1,033	1,026
Retained Earnings	6,525	6,041	6,044
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts Receivable, net			2,025
Prepaid Expenses and Other Current Assets			224
Deferred Income Taxes			2,008
Accounts Payable — Trade			2,807
Other Current Liabilities			1,026
Retained Earnings			$ 6,044
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts Receivable, net	2,658
Prepaid Expenses and Other Current Assets	238
Deferred Income Taxes	1,909
Accounts Payable — Trade	2,810
Other Current Liabilities	784
Retained Earnings	6,523
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts Receivable, net	12	3
Prepaid Expenses and Other Current Assets	11	7
Deferred Income Taxes	(1)	1
Accounts Payable — Trade	9	7
Other Current Liabilities	11	7
Retained Earnings	$ 2	$ (3)