Financial Instruments (Narrative 1) (Details)	Sep. 30, 2011	Dec. 31, 2010
Derivative power contracts in PJM Power Pool [Member] | GWh (thousand megawatt hours of power) [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	1,700	1,700
Derivative power contracts related to installed capacity in PJM Power Pool [Member] | GW (gigawatts of power) [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	71	71
Natural gas contracts with expiration date 2019, low end [Member] | MMBtu/d million British thermal units of natural gas [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	12,550	12,550
Natural gas contracts with expiration date 2019, high end [Member] | MMBtu/d million British thermal units of natural gas [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	95,000	95,000
Derivative power contracts with swaps, low end [Member] | GWh (thousand megawatt hours of power) [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	1,700	1,700
Derivative power contracts with swaps, high end [Member] | GWh (thousand megawatt hours of power) [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	3,700	3,700
MBbl (thousand barrels of oil) [Member] | Oil [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	15,956	12,240
TBtu (trillion British thermal units of natural gas) [Member] | Natural Gas [Member]
Component of Other Income, Nonoperating [Line Items]
Derivative, nonmonetary notional amount	149	283