Supplementary Financial Information - Restricted Cash Balance Sheet Location (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	$ 55	$ 55
Other current assets
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	16	0
Other long-term assets
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	$ 39	$ 55