Regulatory Assets and Liabilities, Regulatory Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[1]	$ 57	$ 118
Regulatory Liability, Noncurrent	[1]	718	732
Other Current Liabilities
Regulatory Liabilities [Line Items]
Entity's Recorded Provision for Revenue Subject To Refund		4
Deferred Income Tax Adjustments and TCJA Refunds
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[2]	6	7
Regulatory Liability, Noncurrent	[2]	513	535
Plant Removal Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		0	0
Regulatory Liability, Noncurrent		177	175
Revenue Subject to Refund
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		4	14
Regulatory Liability, Noncurrent		4	1
Gain From Asset Sales
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		0	0
Regulatory Liability, Noncurrent		2	2
Deferred Electric Energy Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		35	82
Regulatory Liability, Noncurrent		0	0
Contract Valuation Adjustments
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[3]	7	12
Regulatory Liability, Noncurrent	[3]	0	0
Other
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		5	3
Regulatory Liability, Noncurrent		$ 22	$ 19
Sales True Up and Revenue Decoupling [Member] | Minimum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		1 year
Sales True Up and Revenue Decoupling [Member] | Maximum [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Amortization Period		2 years

[1] Revenue subject to refund of $4 million for 2019 was included in other current liabilities and none for 2020.

[2] Includes the revaluation of recoverable/regulated plant ADIT and revaluation impact of non-plant ADIT due to the TCJA.

[3] Includes costs for conservation programs, as well as incentives allowed in certain jurisdictions.