Supplemental Cash Flow Information Reconciliation to Statement of Cash Flows (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 196	$ 182	$ 288	$ 245	$ 277	$ 323	$ 206	$ 220	$ 314
Restricted cash	137	138	136	158	131	125	125	120	121
Restricted Cash, Noncurrent	5				5				5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 338	$ 325	$ 429	$ 408	$ 413	$ 453	$ 336	$ 345	$ 440	$ 697

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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