Commitments and Contingencies (Details) $ in Millions		3 Months Ended	9 Months Ended
	Jun. 01, 2001	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2018 facility	Aug. 18, 2016 USD ($)
Commonwealth Edison Company And Exelon Generation Company LLC
Loss Contingencies
Payment for litigation settlement		$ 26.0
CDWR and SDGE v Sunrise Power
Loss Contingencies
PPA period	10 years
Damages sought, amount			$ 1.2
Remaining term			70 months
Sierra Club Et Al V. Midwest Generation LLC
Loss Contingencies
Number of facilities | facility				4
Lignite Contract With Texas Westmoreland Coal Co.
Loss Contingencies
Bond obligation					$ 99.0