Balance Sheet Components Allowance for Uncollectible accounts activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance as of beginning of year	$ 5	$ 15	$ 6
Increase in provision	15	2	14
Amounts written off, less recoveries	(4)	(12)	(5)
Balance as of end of year	16	$ 5	$ 15
OPUC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in provision	$ 8