Related Party Transactions (Schedule Of Related Party Transactions) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Ownership interest in partnership	3.50%		3.50%
Partnership (Director Ownership Interest) [Member]
Related Party Transaction [Line Items]
Amounts paid	$ 1	$ 1	$ 5	$ 3