Basis of Presentation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) mi² shares retail_customers	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Basis of Presentation [Abstract]
Service Area Sq Miles | mi²	4,000,000
Incorporated Cities	51
Number of Retail Customers | retail_customers	908,000
Service area population	1,900,000
Entity Number of Employees	3,639
Number of Union Employees	721
Number of Union Employees Subject to Agreement A	660
Number of Union Employees Subject to Agreement B	61
Share-based Payment Arrangement, Noncash Expense | $	$ 11	$ 9	$ 5