Supplemental Cash Flow Information (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Cash paid for or (received from):
Cash and cash equivalents	$ 185	$ 280	$ 255	$ 224
Restricted cash	89	89	89	89
Cash and Cash Equivalents Including Restricted Cash, at Carrying Value	$ 274	$ 368	$ 344	$ 313