Derivative Instruments and Hedging Activities (Details 2)	Jun. 30, 2011	Dec. 31, 2010
Electric Utility | Economic hedges | Electricity options, swaps and forwards in gigawatts per hour (GWh)
Derivatives
Notional Volumes of Derivative Instruments	34,471	32,138
Electric Utility | Economic hedges | Natural gas options, swaps and forwards, Bcf
Derivatives
Notional Volumes of Derivative Instruments	255	250
Electric Utility | Economic hedges | CRRs
Derivatives
Notional Volumes of Derivative Instruments	147,992	181,291
Electric Utility | Economic hedges | Tolling arrangements (GWh)
Derivatives
Notional Volumes of Derivative Instruments	105,631	114,599
Competitive power generation | Cash flow hedges | Electricity Forwards/Futures, Sales, GWh
Derivatives
Notional Volumes of Derivative Instruments	18,901	16,799
Competitive power generation | Cash flow hedges | Electricity Forwards/Futures, Purchases, GWh
Derivatives
Notional Volumes of Derivative Instruments	203	408
Competitive power generation | Cash flow hedges | Electricity Capacity, Sales, MW-Day (in thousands)
Derivatives
Notional Volumes of Derivative Instruments	171,000	190,000
Competitive power generation | Cash flow hedges | Electricity Capacity, Purchases, MW-Day (in thousands)
Derivatives
Notional Volumes of Derivative Instruments	17,000	8,000
Competitive power generation | Economic hedges | Electricity Forwards/Futures, Sales, GWh
Derivatives
Notional Volumes of Derivative Instruments	17,660	22,456
Competitive power generation | Economic hedges | Electricity Forwards/Futures, Purchases, GWh
Derivatives
Notional Volumes of Derivative Instruments	17,750	22,931
Competitive power generation | Economic hedges | Electricity Congestion, Sales, GWh
Derivatives
Notional Volumes of Derivative Instruments	124	136
Competitive power generation | Economic hedges | Electricity Congestion, Purchases, GWh
Derivatives
Notional Volumes of Derivative Instruments	5,459	1,143
Competitive power generation | Economic hedges | Natural Gas Forwards/Futures, Sales, billion cubic feet
Derivatives
Notional Volumes of Derivative Instruments	1.5
Competitive power generation | Economic hedges | Natural Gas Forwards/Futures, Purchases, billion cubic feet
Derivatives
Notional Volumes of Derivative Instruments	1.5
Competitive power generation | Economic hedges | Fuel Oil Forwards/Futures, Sales, Barrels
Derivatives
Notional Volumes of Derivative Instruments		250,000
Competitive power generation | Economic hedges | Fuel Oil Forwards/Futures, Purchases, Barrels
Derivatives
Notional Volumes of Derivative Instruments	240,000	490,000
Competitive power generation | Trading activities | Electricity Forwards/Futures, Sales, GWh
Derivatives
Notional Volumes of Derivative Instruments	39,629	34,630
Competitive power generation | Trading activities | Electricity Forwards/Futures, Purchases, GWh
Derivatives
Notional Volumes of Derivative Instruments	42,863	37,669
Competitive power generation | Trading activities | Electricity Capacity, Sales, MW-Day (in thousands)
Derivatives
Notional Volumes of Derivative Instruments	17,000	136,000
Competitive power generation | Trading activities | Electricity Capacity, Purchases, MW-Day (in thousands)
Derivatives
Notional Volumes of Derivative Instruments	247,000	419,000
Competitive power generation | Trading activities | Electricity Congestion, Sales, GWh
Derivatives
Notional Volumes of Derivative Instruments	14,314	12,020
Competitive power generation | Trading activities | Electricity Congestion, Purchases, GWh
Derivatives
Notional Volumes of Derivative Instruments	287,221	187,689
Competitive power generation | Trading activities | Natural Gas Forwards/Futures, Sales, billion cubic feet
Derivatives
Notional Volumes of Derivative Instruments	354.1	30.6
Competitive power generation | Trading activities | Natural Gas Forwards/Futures, Purchases, billion cubic feet
Derivatives
Notional Volumes of Derivative Instruments	351.8	34.3
Competitive power generation | Trading activities | Fuel Oil Forwards/Futures, Sales, Barrels
Derivatives
Notional Volumes of Derivative Instruments	45,000	10,000
Competitive power generation | Trading activities | Fuel Oil Forwards/Futures, Purchases, Barrels
Derivatives
Notional Volumes of Derivative Instruments	70,000	10,000
Competitive power generation | Trading activities | Coal Forwards/Futures, Sales, tons
Derivatives
Notional Volumes of Derivative Instruments	2,564,250	2,630,500
Competitive power generation | Trading activities | Coal Forwards/Futures, Purchases, tons
Derivatives
Notional Volumes of Derivative Instruments	2,564,250	2,645,500