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Balance Sheet Components Allowance for Uncollectible accounts activity (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Balance as of beginning of year $ 6us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 5us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 6us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Increase in provision 6us-gaap_ProvisionForDoubtfulAccounts 6us-gaap_ProvisionForDoubtfulAccounts 6us-gaap_ProvisionForDoubtfulAccounts
Amounts written off, less recoveries (6)us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs (5)us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs (7)us-gaap_AllowanceForDoubtfulAccountsReceivableWriteOffs
Balance as of end of year $ 6us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 6us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 5us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent