Balance Sheet Components (Details)		3 Months Ended
	Apr. 12, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Letters of Credit Outstanding, Amount		$ 0
Finite-Lived Intangible Assets, Accumulated Amortization		318,000,000		$ 302,000,000
Amortization of Intangible Assets		$ 16,000,000	$ 13,000,000
Line of Credit Facility, Maximum Borrowing Capacity				500,000,000
Debt Instrument, Covenant Description		0.65
Ratio of Indebtedness to Net Capital		0.493
Short-term debt		$ 0
Commercial Paper		0
Line of Credit Facility, Remaining Borrowing Capacity		500,000,000
Line of Credit Facility, Current Borrowing Capacity		220,000,000
Letters of credit issued		83,000,000
Authorized Short-Term Debt		900,000,000
Long-term Debt, Current Maturities		$ 300,000,000		$ 300,000,000
Subsequent Event [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Proceeds from Issuance of Long-term Debt	$ 200,000,000