Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Depreciation expense expressed as a percentage of average depreciable property	3.20%	3.10%	2.90%
Cash and Cash Equivalents [Abstract]
Maximum number of months remaing	$ 3
Accounts and Financing Receivable, after Allowance for Credit Loss, Current and Noncurrent [Abstract]
Accounts Receivable, Allowance for Credit Loss, Current	$ 40,000,000	$ 29,000,000
Alternative Revenue Programs [Abstract]
Number of DSM Products, Commercial and Industrial Customers	20
Number of DSM Products, Residential and Low-income Customers	23
maximum number of months following end of annual period in which revenues are to be included	$ 24
DSM Measurements	1,000
Public Utilities, Inventory [Line Items]
Inventories	$ 245,000,000	189,000,000
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	70,000,000	63,000,000
Public Utilities, Inventory, Fuel [Member]
Public Utilities, Inventory [Line Items]
Inventories	71,000,000	73,000,000
Public Utilities, Inventory, Natural Gas [Member]
Public Utilities, Inventory [Line Items]
Inventories	$ 104,000,000	$ 53,000,000