Revenue Recogniton Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Document Period End Date	Dec. 31, 2020
Regulated Operating Revenue, Electric, Non-Nuclear	$ 1,910	$ 1,857
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price	(6)	2	$ 3
Deferred Revenue, Revenue Recognized	28	22
Regulated Operating Revenue	1,932	1,881
Unregulated Operating Revenue	162	170
Regulated and Unregulated Operating Revenue	51	72
Total Revenues	2,145	2,123	1,991
Gain on Derivative Instruments, Pretax	65	50
Asset Retirement Obligation, Cash Paid to Settle	18	9	$ 5
Residential [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	1,030	981
Commercial [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	616	636
Industrial [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	218	196
Direct Access customers [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	46	44
Revenue Subject to Refund [Member]
Disaggregation of Revenue [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 24	$ 23