Basis of Presentation (Details) retail_customers in Thousands, mi² in Thousands, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019 USD ($) mi² retail_customers	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) mi² retail_customers	Jun. 30, 2018 USD ($)
Basis of Presentation [Abstract]
Service Area Sq Miles | mi²	4,000			4,000
Incorporated Cities	51			51
Number of Retail Customers | retail_customers	888			888
Percent of state population	46.00%			46.00%
Alternative revenue programs, net of amortization	$ (2)		$ 0	$ 1	$ (2)
Reclassification of stranded tax effects due to Tax Reform		$ 0		2
Property, Plant and Equipment [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				(178)
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				44
Accounting Standards Update 2016-02 [Member] | Property, Plant and Equipment [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				2
Building [Member] | Property, Plant and Equipment [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				131
Assets Held under Capital Leases [Member] | Property, Plant and Equipment [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				$ 49