Balance Sheet Components (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended					9 Months Ended
	Dec. 31, 2013	Nov. 30, 2013	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	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
Expenses related to Cascade Crossing				0		0		52	0
Sale Leaseback Transaction, Construction Cost							10
Finite-Lived Intangible Assets, Accumulated Amortization				167				167		151
Amortization of Intangible Assets				5		5		16	17
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
Line of Credit Facility, Current Borrowing Capacity	60.0		60.0	51.5				51.5
letter of credit facility	30.0		30.0	21.5				21.5
Authorized Short-Term Debt				700				700
Borrowings				0				0
Letters of Credit Issued				56				56
Line of Credit Facility, Remaining Borrowing Capacity				696				696
Commercial Paper				0				0
Repayments of Long-term Debt				50	50			100	0
Proceeds from Issuance of Long-term Debt	$ 50	$ 105	$ 155	$ 75	$ 150			$ 225	$ 0