Short-term Borrowings and Other Debt Obligations Schedule of Borrowing Availability (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Credit agreement, maximum capacity	$ 1,144
Line of Credit Facility, Remaining Borrowing Capacity	93
A&R Credit Agreement
Line of Credit Facility [Line Items]
Short-term debt	230	$ 0
364 Day Secured RCF [Member]
Line of Credit Facility [Line Items]
Short-term debt	317	$ 317
Committed Letters of Credit [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding, Amount	206
Term Loan Borrowings before Debt Issuance Cost [Member]
Line of Credit Facility [Line Items]
Debt and Capital Lease Obligations	$ 298