Short-term Borrowings and Other Debt Obligations Line of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,375
Debt and Capital Lease Obligations	7,678	$ 7,580
Line of Credit Facility, Remaining Borrowing Capacity	890
Committed Letters of Credit [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	110
Term Loan Borrowings before Debt Issuance Cost [Member]
Line of Credit Facility [Line Items]
Debt and Capital Lease Obligations	$ 375