Basis of Presentation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) mi² shares retail_customers	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Basis of Presentation [Abstract]
Service Area Sq Miles | mi²	4,000
Incorporated Cities	51
Number of Retail Customers | retail_customers	895,000
Service area population	1,900,000
Entity Number of Employees	2,949
Number of Union Employees	775
Number of Union Employees Subject to Agreement A	719
Number of Union Employees Subject to Agreement B	56
Share-based Payment Arrangement, Noncash Expense | $	$ 9	$ 5	$ 7