Balance Sheet Components (Details) - USD ($)		3 Months Ended			6 Months Ended
	Jan. 09, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	May 04, 2016	Jan. 31, 2016	Jan. 11, 2016	Jan. 08, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization		$ 249,000,000			$ 249,000,000						$ 227,000,000
Amortization of Intangible Assets		10,000,000		$ 9,000,000	22,000,000	$ 18,000,000
Syndicated credit facility scheduled to expire in 2019		500,000,000			500,000,000
Line of Credit Facility, Current Borrowing Capacity		$ 160,000,000			$ 160,000,000
Debt Instrument, Covenant Description					0.65
Ratio of Indebtedness to Net Capital		0.511			0.511
Short-term debt		$ 0			$ 0						$ 6,000,000
Line of Credit Facility, Remaining Borrowing Capacity		500,000,000			500,000,000
Letters of credit issued		92,000,000			92,000,000
Authorized Short-Term Debt		$ 900,000,000			$ 900,000,000
Debt Instrument, Redemption, Description		75			200
Unsecured term bank loan rate - minimum		0.00%			0.00%
Proceeds from Issuance of Long-term Debt		$ 75,000,000			$ 75,000,000		$ 50,000,000			$ 140,000,000
Debt Instrument, Interest Rate, Stated Percentage								3.81%	5.80%	2.51%
Extinguishment of Debt, Amount			$ 133,000,000		133,000,000	$ 387,000,000
Capital Leases, Future Minimum Payments, Remainder of Fiscal Year		$ 3,000,000			$ 3,000,000
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