Balance Sheet Components Allowance for Uncollectible accounts activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance as of beginning of year	$ 6	$ 6	$ 6
Increase in provision	5	6	6
Amounts written off, less recoveries	(5)	(6)	(6)
Balance as of end of year	$ 6	$ 6	$ 6