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Customer Financing (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Customer Financing [Line Items]    
Individually evaluated for impairment $ 77 $ 55
Impaired financing receivables 66 $ 44
Average recorded investment in impaired receivables $ 46  
B Credit Rating [Member]    
Customer Financing [Line Items]    
Percentage Of Credit Default Rates Applied To Customers 22.60%  
BB Credit Rating [Member]    
Customer Financing [Line Items]    
Percentage Of Credit Default Rates Applied To Customers 4.70%  
BBB Credit Rating [Member]    
Customer Financing [Line Items]    
Percentage Of Credit Default Rates Applied To Customers 0.90%