Summary of Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Depreciation expense expressed as a percentage of average depreciable property	3.30%	3.10%	2.90%
Cash and Cash Equivalents [Abstract]
cash and cash equivalents	$ 3
Accounts and Financing Receivable, after Allowance for Credit Loss, Current and Noncurrent [Abstract]
Accounts Receivable, Allowance for Credit Loss, Current	12,000,000	$ 8,000,000
Alternative Revenue Programs [Abstract]
maximum number of months following end of annual period	24
Public Utilities, Inventory [Line Items]
Inventory	51,000,000	36,000,000
Supplies
Public Utilities, Inventory [Line Items]
Inventory	29,000,000	27,000,000
Fuel
Public Utilities, Inventory [Line Items]
Inventory	$ 22,000,000	$ 9,000,000