Acquisitions - Thunderhead (Details) - Thunderhead Wind Energy LLC $ in Millions	1 Months Ended
	Aug. 31, 2019 MW	Feb. 19, 2020 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Capacity of generation unit | MW	300
Duration of offtake agreement for the sale of energy produced	12 years
Bonus depreciation percentage	100.00%
WECI
Business Acquisition [Line Items]
Ownership interest in wind generating facility acquired	80.00%
Acquisition purchase price			$ 338
Subsequent event | WECI
Business Acquisition [Line Items]
Acquisition purchase price		$ 43
Additional ownership interest acquired		10.00%