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Related Party Transactions (Schedule Of Related Party Transactions) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Related Party Transaction [Line Items]        
Ownership interest in partnership 3.50%      
Partnership (Director Ownership Interest) [Member]        
Related Party Transaction [Line Items]        
Amounts paid $ 2 $ 1 $ 4 $ 2