Balance Sheet Components (Details) $ in Millions				3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Aug. 11, 2021 USD ($)	Jan. 06, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Apr. 09, 2020 USD ($)
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Accounts Receivable, Allowance for Credit Loss	$ 27			$ 27		$ 27		$ 22		$ 16
Unbilled Receivables, Current	80			80		80				97
Finite-Lived Intangible Assets, Accumulated Amortization	432			432		432				388
Amortization of Intangible Assets				14	$ 16	44	$ 47
Line of Credit Facility, Maximum Borrowing Capacity	$ 750			$ 750		$ 750
Debt Instrument, Covenant Description						65.00%
Ratio of Indebtedness to Net Capital	0.564			0.564		0.564
Short-term debt	$ 0			$ 0		$ 0			$ 200	150	$ 150
Line of Credit Facility, Remaining Borrowing Capacity	650			650		650
Line of Credit Facility, Current Borrowing Capacity	220			220	650	220	650
Letters of credit issued	78			78		78
Authorized Short-Term Debt	900			900		900
Long-term Debt, Current Maturities	0			0		0				160
Proceeds from Issuance of Long-term Debt	400					400	319
Purchased power and fuel				259	$ 292	613	554
Repayments of Long-term Debt		$ 20	$ 140			160	$ 98
Operating Lease, Right-of-Use Asset	140			140		140
Amount above baseline net variable power costs						60
Lower deadband limit below baseline net variable power costs						15
Upper deadband limit above baseline net variable power costs						30
Issuance of 2028 Bonds	100
Issuance of 2031 Bonds	50
Issuance of 2034 Bonds	100
Issuance of 2051 Bonds	150
221119 Other Electric Power Generation
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Increase (Decrease) in Accounts Payable and Other Operating Liabilities	27			27		27				0
Fire
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Increase (Decrease) in Accounts Payable and Other Operating Liabilities	36			36		36				15
pandemic
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Increase (Decrease) in Accounts Payable and Other Operating Liabilities	27			27		27				$ 10
Letter of Credit [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Short-term debt	$ 0			$ 0		$ 0