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Balance Sheet Components Allowance for Uncollectible accounts activity (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance as of beginning of year	$ 6	$ 5	$ 5
Increase in provision	6	11	7
Allowance for Doubtful Accounts Receivable, Charge-offs	(7)	(10)	(7)
Balance as of end of year	$ 5	$ 6	$ 5

Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected).

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