Balance Sheet Components (Details)	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Apr. 09, 2020 USD ($)	Mar. 11, 2020 USD ($)	Dec. 31, 2019 USD ($)
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts Receivable, Allowance for Credit Loss	$ 6,000,000				$ 5,000,000
Unbilled Receivables, Current	78,000,000				86,000,000
Finite-Lived Intangible Assets, Accumulated Amortization	381,000,000				366,000,000
Amortization of Intangible Assets	$ 15,000,000	$ 16,000,000
Line of Credit Facility, Maximum Borrowing Capacity					500,000,000
Debt Instrument, Covenant Description	65.00%
Ratio of Indebtedness to Net Capital	0.504
Short-term debt	$ 20,000,000				0
Line of Credit Facility, Remaining Borrowing Capacity	480,000,000
Line of Credit Facility, Current Borrowing Capacity	220,000,000
Letters of credit issued	51,000,000
Authorized Short-Term Debt	900,000,000
Long-term Debt, Current Maturities	140,000,000				$ 0
Proceeds from Issuance of Long-term Debt	119,000,000	$ 0
Long-term Pollution Control Bond				$ 119,000,000
Letter of Credit [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Short-term debt	$ 20,000,000
Member one [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Long-term Pollution Control Bond				98,000,000
Member 2 [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Long-term Pollution Control Bond				$ 21,000,000
Subsequent Event [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Short-term debt			$ 150,000,000