Revenue Recogniton Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Document Period End Date	Dec. 31, 2019
Regulated Operating Revenue, Electric, Non-Nuclear	$ 1,857	$ 1,823
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price	2	3	$ 0
Deferred Revenue, Revenue Recognized	(22)	(45)
Regulated Operating Revenue	1,881	1,781
Unregulated Operating Revenue	170	159
Regulated and Unregulated Operating Revenue	72	51
Total Revenues	2,123	1,991	$ 2,009
Gain on Derivative Instruments, Pretax	50	42
Residential [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	981	948
Commercial [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	636	647
Industrial [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	196	185
Direct Access customers [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Electric, Non-Nuclear	44	43
Revenue Subject to Refund [Member]
Disaggregation of Revenue [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 23	$ 45