Supplemental Cash Flow Information (Summary Of Cash And Cash Equivalents And Restricted Cash) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 288	$ 280	$ 140	$ 224
Restricted cash	89	89	89	89
Total Cash and cash equivalents and Restricted cash	$ 377	$ 368	$ 228	$ 313