Balance Sheet Components (Details)		3 Months Ended
	Jan. 09, 2016 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Jan. 31, 2016	Jan. 11, 2016	Jan. 08, 2016 USD ($)	Dec. 31, 2015 USD ($)
Valuation and Qualifying Accounts Disclosure [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization		$ 238,000,000					$ 227,000,000
Amortization of Intangible Assets		11,000,000	$ 9,000,000
Syndicated credit facility scheduled to expire in 2019		500,000,000
Line of Credit Facility, Current Borrowing Capacity		$ 160,000,000
Debt Instrument, Covenant Description		.65
Ratio of Indebtedness to Net Capital		0.499
Short-term debt		$ 0					$ 6,000,000
Line of Credit Facility, Remaining Borrowing Capacity		500,000,000
Letters of credit issued		111,000,000
Authorized Short-Term Debt		900,000,000
Proceeds from Issuance of Long-term Debt						$ 140,000,000
Debt Instrument, Interest Rate, Stated Percentage				3.81%	5.80%	2.51%
Extinguishment of Debt, Amount		133,000,000	$ 120,000,000
Capital Leases, Future Minimum Payments, Remainder of Fiscal Year		$ 5,000,000
Notes Payable to Banks [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Extinguishment of Debt, Amount	$ 75,000,000
Long-term Debt [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Extinguishment of Debt, Amount	$ 58,000,000