Supplementary Financial Information - Restricted Cash Balance Sheet Location (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	$ 82	$ 66
Other current assets
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	44	23
Other long-term assets
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	$ 38	$ 43