Balance Sheet Components (Details) $ in Millions		3 Months Ended		9 Months Ended
	Apr. 27, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	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		$ 14		$ 14		$ 12			$ 5
Unbilled Receivables, Current		79		79					86
Finite-Lived Intangible Assets, Accumulated Amortization		403		403					366
Amortization of Intangible Assets		16	$ 16	47	$ 49
Line of Credit Facility, Maximum Borrowing Capacity		$ 600		$ 600
Debt Instrument, Covenant Description				65.00%
Ratio of Indebtedness to Net Capital		0.555		0.555
Short-term debt		$ 225		$ 225			$ 150		0
Line of Credit Facility, Remaining Borrowing Capacity		500		500
Line of Credit Facility, Current Borrowing Capacity		220	500	220	500
Letters of credit issued		55		55
Authorized Short-Term Debt		900		900
Long-term Debt, Current Maturities		160		160					$ 0
Proceeds from Issuance of Long-term Debt				319	200
Long-term Pollution Control Bond								$ 119
Proceeds from Issuance of Debt	$ 200
Purchased power and fuel		292	$ 165	554	$ 449
Derivative Instruments Not Designated as Hedging Instruments, Loss		127
Excess Net Variable Power Costs				70
Letter of Credit [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Short-term debt		$ 75		$ 75
Member one [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Long-term Pollution Control Bond								98
Member 2 [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Long-term Pollution Control Bond								$ 21