Acquisitions and Dispositions - Schedule of Acquisition (Details) - SOUTHERN POWER CO - Diamond State Generation Partners $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019 MW	Aug. 31, 2019 MW	Sep. 30, 2019 USD ($) MW
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	28		28
PPA Contract Period	15 years
Purchase price | $			$ 166
Percentage of operating results consolidated	100.00%
Noncontrolling interest, approximate nameplate capacity	10		10
Approximate nameplate capacity, repowered amount		18
Diamond State Generation Partners | Common Class B
Business Acquisition [Line Items]
Ownership percentage by parent	100.00%		100.00%