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Revenue (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Change in Contract with Customer, Asset [Abstract]    
Beginning balance $ 89  
Additions, net 38  
Billings (34)  
Other 1  
Ending balance 94  
Change in Contract with Customer, Liability [Abstract]    
Beginning balance 107  
Additions, net   $ 56
Revenue recognized from opening balance   (54)
Other   $ 1
Ending balance $ 110