Commitments, Guarantees and Contingencies - Clean Air Act and Climate Change (Details) T in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 phase T	Dec. 31, 2018 USD ($)	Nov. 12, 2014
Loss Contingencies [Line Items]
Proposed reduction in power plants carbon pollution (percent)	90.00%
National Ambient Air Quality Standards
Loss Contingencies [Line Items]
Capping of SO2 Emissions Under CSAPR	2.4
Capping of NOx emissions under CSAPR	1.2
National Ambient Air Quality Standards | CSAPR
Loss Contingencies [Line Items]
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides | phase	2
Minimum | Climate Change
Loss Contingencies [Line Items]
Reduction in emissions (percent)			26.00%
Maximum | Climate Change
Loss Contingencies [Line Items]
Reduction in emissions (percent)			28.00%
Discontinued Operations, Disposed of by Means Other than Sale | FES and FENOC
Loss Contingencies [Line Items]
Amount of damages awarded to other party | $		$ 66