Balance Sheet Components (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts Receivable, Current	$ 7,000,000	$ 5,000,000	$ 7,000,000	$ 5,000,000	$ 6,000,000	$ 5,000,000
Finite-Lived Intangible Assets, Accumulated Amortization	182,000,000		182,000,000		170,000,000
Amortization of Intangible Assets	6,000,000	6,000,000	12,000,000	11,000,000
Expenses related to Cascade Crossing	0	52,000,000	0	52,000,000
Line of Credit Facility scheduled to terminate in 2017	400,000,000		400,000,000
Credit Facilities - $300 million revolver	300,000,000		300,000,000
Debt Instrument, Covenant Description			.65
Ratio of Indebtedness to Net Capital	0.534		0.534
Authorized Short-Term Debt	900,000,000		900,000,000
Short-term Debt	0		0
Commercial Paper	0		0
Borrowings	9,000,000		9,000,000
Line of Credit Facility, Remaining Borrowing Capacity	691,000,000		691,000,000
Line of Credit Facility, Current Borrowing Capacity	30,000,000		30,000,000
Pledged Financial Instruments, Not Separately Reported, Securities for Letter of Credit Facilities	54,000,000		54,000,000
letter of credit facility amount available	6,000,000		6,000,000
Proceeds from Long-term Lines of Credit			305,000,000
Debt Instrument, Description of Variable Rate Basis			70
Debt Instrument, Interest Rate During Period	0.90%
Debt [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Issuance of Long-term Debt	280,000,000		280,000,000
4.35%, May 15 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Long-term Lines of Credit			75,000,000
4.45%, May 30 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Long-term Lines of Credit			75,000,000
4.45%, June 30 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Long-term Lines of Credit			75,000,000
July 31 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Long-term Lines of Credit			80,000,000
4.39%, August 15, 2014 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Issuance of Long-term Debt	100,000,000		100,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.39%		4.39%
4.44%, October 15, 2014 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Issuance of Long-term Debt	100,000,000		100,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.44%		4.44%
3.51%, November 17, 2014 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Issuance of Long-term Debt	$ 80,000,000		$ 80,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.51%		3.51%