Balance Sheet Components (Details) - USD ($)		3 Months Ended				6 Months Ended
	May. 22, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	May. 21, 2015	May. 19, 2015	Jan. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]
Asset Retirement Obligations, Significant Changes			15
Allowance for Doubtful Accounts Receivable, Current			$ 6,000,000		$ 7,000,000	$ 6,000,000	$ 7,000,000				$ 6,000,000	$ 6,000,000
Finite-Lived Intangible Assets, Accumulated Amortization			209,000,000			209,000,000					191,000,000
Amortization of Intangible Assets			9,000,000		$ 6,000,000	18,000,000	12,000,000
Syndicated credit facility scheduled to expire in 2018			$ 500,000,000			$ 500,000,000
Line of Credit Facility, Current Borrowing Capacity				$ 500,000,000							$ 700,000,000
Debt Instrument, Covenant Description						.65
Ratio of Indebtedness to Net Capital			0.5			0.5
Short-term Debt			$ 0			$ 0
Borrowings			38,000,000			38,000,000
Line of Credit Facility, Remaining Borrowing Capacity			462,000,000			462,000,000
Letters of Credit Outstanding, Amount			30,000,000			30,000,000
Letters of credit issued			59,000,000			59,000,000
Authorized Short-Term Debt			$ 900,000,000			$ 900,000,000
Debt Instrument, Interest Rate, Stated Percentage			3.46%			3.46%		6.80%	3.50%	3.55%
Extinguishment of Debt, Amount						$ 387,000,000	$ 0
[Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Issuance of Long-term Debt				75,000,000					$ 70,000,000
Notes Payable to Banks [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Extinguishment of Debt, Amount	$ 67,000,000		$ 200,000,000	$ 50,000,000
Long-term Debt [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Extinguishment of Debt, Amount						$ 70,000,000
Subsequent Event [Member] | Notes Payable to Banks [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Extinguishment of Debt, Amount		$ 55,000,000