Balance Sheet Components (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended		9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts Receivable, Current		$ 5	$ 6		$ 5	$ 6		$ 5	$ 6
Finite-Lived Intangible Assets, Accumulated Amortization		162			162			151
Amortization of Intangible Assets		6	6		11	11
Sale Leaseback Transaction, Construction Cost				10
Line of Credit Facility scheduled to terminate in 2017		400			400
Credit Facilities - $300 million revolver		300			300
Debt Instrument, Covenant Description					.65
Ratio of Indebtedness to Net Capital		0.496			0.496
letter of credit facility		21.5			21.5
Authorized Short-Term Debt		700			700
Borrowings		0			0
Letters of Credit Issued		54			54
Line of Credit Facility, Remaining Borrowing Capacity		668			668
Commercial Paper		0			0
Repayments of Long-term Debt		50			50	0
Proceeds from Issuance of Long-term Debt	$ 75	$ 150			$ 150	$ 0	$ 225