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Summary of Significant Accounting Policies (Schedule of Trade Receivable) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Summary of trade receivables, net        
Trade receivables $ 1,680 $ 1,747    
Allowance for doubtful accounts (41) (16) $ (16) $ (16)
Total trade receivables, net 1,639 1,731    
Billed Revenues        
Summary of trade receivables, net        
Trade receivables 1,452 1,546    
Unbilled Revenues        
Summary of trade receivables, net        
Trade receivables $ 228 $ 201