Summary of Significant Accounting Policies Operating Revenues (Details)	12 Months Ended
	Dec. 31, 2019 contract performance_obligations
Electric
Disaggregation of Operating Revenues
Number of performance obligations	1
Percent fuel costs can vary from the rate case approved costs before deferral is required	2.00%
Number of days payment is due	30 days
Electric | Wholesale
Disaggregation of Operating Revenues
Number of performance obligations	2
Number of contracts | contract	1
Natural gas
Disaggregation of Operating Revenues
Number of days payment is due	30 days