Supplementary Financial Information - Restricted Cash Balance Sheet Location (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	$ 64	$ 64
Other current assets
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	0	1
Other long-term assets
Restricted Cash and Cash Equivalents Items [Line Items]
Total Restricted cash	$ 64	$ 63