Revenue - Narrative Revenue Term (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01	Mar. 31, 2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Auction period	9 months
Transmission congestion contracts | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Auction period	6 months
Transmission congestion contracts | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Auction period	2 years