Operations and Significant Accounting Policies - Concentration of Credit Risk (Details) - Customer Concentration Risk [Member] - Large Power Customers [Member] $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Customers	Dec. 31, 2019 USD ($) Customers	Dec. 31, 2018 Customers
Concentration Risk [Line Items]
Number of Large Power Customers	8	9	9
Receivables from Large Power Customers | $	$ 10.3	$ 7.8
Number of entities	2
Largest Customer [Member] | Consolidated Operating Revenue [Member]
Concentration Risk [Line Items]
Percent of Operating Revenue	25.00%	12.00%	10.00%
Largest Customer [Member] | Consolidated Operating Revenue [Member] | Regulated Operations [Member]
Concentration Risk [Line Items]
Percent of Operating Revenue	29.00%