Commitments, Guarantees and Contingencies - Clean Air Act and Climate Change (Details) $ in Millions			1 Months Ended	12 Months Ended		48 Months Ended
	Oct. 01, 2015	Aug. 03, 2015 T	Aug. 31, 2015	Dec. 31, 2015 USD ($) phase T	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) T	Apr. 30, 2015 MW	Nov. 12, 2014	Apr. 30, 2014	Jun. 30, 2013
Year 2020
Loss Contingencies [Line Items]
Reduction in power plants carbon pollution, (percent)										17.00%
FES
Loss Contingencies [Line Items]
Loss Contingency, Damages Paid, Value					$ 70
National Ambient Air Quality Standards
Loss Contingencies [Line Items]
Capping of SO2 Emissions Under CSAPR | T				2,400,000
Capping of NOx emissions under CSAPR | T				1,200,000
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
Hazardous Air Pollutant Emissions
Loss Contingencies [Line Items]
Potential cost of compliance, MATS				$ 345		$ 345
Hazardous Air Pollutant Emissions | CES
Loss Contingencies [Line Items]
Potential cost of compliance, MATS				168		168
Hazardous Air Pollutant Emissions | Regulated Distribution
Loss Contingencies [Line Items]
Potential cost of compliance, MATS				$ 177		177
Caa Compliance
Loss Contingencies [Line Items]
Loss in period						$ 202
Deactivated Power Plants, Coal-Fired, Capacity | MW							5,429
Mass remaining under contract | T				6,000,000		6,000,000
Caa Compliance | CES
Loss Contingencies [Line Items]
Loss in period						$ 80
Caa Compliance | Regulated Distribution
Loss Contingencies [Line Items]
Loss in period						$ 122
Mercury and Air Toxic Standards | FG | Certain Coal-Fired Power Plant
Loss Contingencies [Line Items]
Loss Contingency, Nonmonetary Contractual Amount in Dispute, Mass | T		3,500,000.0
Mercury and Air Toxic Standards | FG | Another Coal-Fired Power Plant
Loss Contingencies [Line Items]
Loss Contingency, Nonmonetary Contractual Amount in Dispute, Mass | T		2,500,000.0
Climate Change
Loss Contingencies [Line Items]
Reduction in GHG emissions between 2005 and 2012 (percent)									10.00%
Anticipated Reduction in Carbon Dioxide Emissions, Percent				25.00%		25.00%
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%
EPA | Caa Compliance
Loss Contingencies [Line Items]
Period of time to implement plan	3 years
State and Local Agencies | Maximum | Climate Change
Loss Contingencies [Line Items]
Potential MATS extension period			2 years