Regulatory Assets and Liabilities, Regulatory Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 31	$ 79
Regulatory Liability, Noncurrent		350	371
Plant Removal Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		0	0
Regulatory Liability, Noncurrent		184	171
Deferred Income Tax Adjustments and TCJA Refunds
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[1]	0	51
Regulatory Liability, Noncurrent	[1]	161	196
Deferred Electric Production And Natural Gas Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		17	17
Regulatory Liability, Noncurrent		1	0
United States Department of Energy Settlement
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		12	10
Regulatory Liability, Noncurrent		0	0
Other
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		2	1
Regulatory Liability, Noncurrent		$ 4	$ 4

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