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Revenue Recognition Accounts Receivable (Details) - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables, Net, Current $ 929 $ 992
Accounts Receivable Related To Contracts With Customers [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables, Net, Current 794 858
Other Accounts Receivable [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables, Net, Current $ 135 $ 134