Short-term Borrowings and Other Debt Obligations Line of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,156
Debt and Capital Lease Obligations	7,662	$ 7,678
Line of Credit Facility, Remaining Borrowing Capacity	325
A&R Credit Agreement [Member]
Line of Credit Facility [Line Items]
Short-term Debt	0
Committed Letters of Credit [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	204
Term Loan Borrowings before Debt Issuance Cost [Member]
Line of Credit Facility [Line Items]
Debt and Capital Lease Obligations	$ 310