Note 6 - Revenue 2 (Details Textual) $ in Millions	Mar. 31, 2023 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01 | Fixed-Price Contract [Member]
Revenue, Remaining Performance Obligation, Amount	$ 511
Revenue, Remaining Performance Obligation, Percentage	65.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01 | Energy Obligations [Member]
Revenue, Remaining Performance Obligation, Amount	$ 170
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01 | Contract Capacity [Member]
Revenue, Remaining Performance Obligation, Amount	$ 100
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	2025 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Contracts with Price Reopeners [Member]
Revenue, Remaining Performance Obligation, Amount	$ 166
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	1 year