Impairment of Long-Lived Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended														3 Months Ended			12 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 FES	Dec. 31, 2011 FES	Dec. 31, 2010 FES	Dec. 31, 2011 Competitive Energy Services Write-down of carrying value	Dec. 31, 2011 Competitive Energy Services Sulfur Dioxide Emission Allowances	Dec. 31, 2011 Competitive Energy Services Sulfur Dioxide Emission Allowances FES	Dec. 31, 2011 Competitive Energy Services Sulfur Dioxide Emission Allowances AE Supply	Dec. 31, 2011 Competitive Energy Services Excessive or Obsolete Inventory	Dec. 31, 2011 Competitive Energy Services Mono-Nitrogen Oxide Emission Allowances	Dec. 31, 2011 Competitive Energy Services Mono-Nitrogen Oxide Emission Allowances FES	Dec. 31, 2011 Competitive Energy Services Mono-Nitrogen Oxide Emission Allowances AE Supply	Mar. 31, 2011 Fremont Energy Center	Mar. 31, 2011 Fremont Energy Center Write-down of carrying value MW	Mar. 31, 2011 Fremont Energy Center Excessive or Obsolete Inventory MW	Dec. 31, 2011 Peaking Facilities	Dec. 31, 2012 Hazardous Air Pollutant Emissions	Feb. 08, 2012 Hazardous Air Pollutant Emissions MW CoalFiredPlants	Dec. 31, 2012 Hazardous Air Pollutant Emissions FES	Dec. 31, 2011 Hazardous Air Pollutant Emissions Competitive Energy Services
Impairment of Long-Lived Assets [Line Items]
Number of coal-fired plants being retired																				9
Coal-fired plants being retired, total capacity (in MW)																				3,349
Impairment of assets related to retirement							$ 311	$ 5			$ 18											$ 334
Estimated total severance benefits																			14		10
Impairments of long-lived assets	0	413	388	0	294	388						6	1	5	11			23
Other asset impairment charges related to emission allowances								$ 16	$ 13	$ 3
Load following capacity (in MW)																544
Peaking capacity (in MW)																	163