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Revenue from Contracts With Customers - Contract balances (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Contract with Customer, Asset and Liability [Abstract]    
Contract Liabilities (Current) $ 52 $ 45
Contract Liabilities (Noncurrent) 6  
Increase (decrease) current 7  
Increase (decrease) noncurrent 6  
Increase (decrease) in contract liabilities 13  
Cash received on contract liabilities 55  
Revenue recognized previously included in contract liabilities current 42  
Revenue recognized from obligations satisfied or partially satisfied in prior periods $ 4  
Maximum    
Contract with Customer, Asset and Liability [Abstract]    
Payment term 1 year