Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense expressed as a percentage of average depreciable property	3.30%	3.10%	3.10%
Nuclear Decommissioning [Abstract]
Minimum amount of time between nuclear decommissioning studies (in years)	3 years
Cash and Cash Equivalents [Abstract]
Maximum number of months of remaining maturity at time of purchase to consider investments in certain instruments as cash equivalents	3 months
Accounts, Notes, Loans and Financing Receivable
Allowance for bad debts	$ 55	$ 55
Alternative Revenue Programs [Abstract]
Maximum number of months following end of annual period in which revenues are earned to be included in incentive programs	24 months
Inventories	$ 544	548
Supplies [Member]
Inventories	270	271
Public Utilities, Inventory, Fuel [Member]
Inventories	191	170
Public Utilities, Inventory, Natural Gas [Member]
Inventories	$ 83	$ 107