Fair Value of Financial Assets and Liabilities Consideration of Credit Risk and Concentrations (Details) - Credit Concentration Risk [Member] $ in Millions	Dec. 31, 2019 USD ($) Counterparty
Derivative [Line Items]
Number of most significant counterparties	10
Municipal or Cooperative Entities or Other Utilities
Derivative [Line Items]
Number of most significant counterparties	9
External Credit Rating, Investment Grade
Derivative [Line Items]
Number of most significant counterparties	8
Credit exposure for the most significant counterparties | $	$ 54.2
Percentage of credit exposure for the most significant counterparties	68.00%
No Investment Grade Ratings from External Credit Rating Agencies
Derivative [Line Items]
Number of most significant counterparties	2
Credit exposure for the most significant counterparties | $	$ 15.8
Percentage of credit exposure for the most significant counterparties	20.00%