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Derivative Instruments and Hedging Activities (Tables)
 6 Months Ended
Jun. 30, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Notional Volumes of Derivative Instruments
The following table summarizes the notional volumes of derivatives used for hedging activities:
 
 
Economic Hedges
Commodity
Unit of Measure
June 30,
2012
 
December 31, 2011
Electricity options, swaps and forwards
GWh
26,597

 
30,881
Natural gas options, swaps and forwards
Bcf
213

 
300
Congestion revenue rights
GWh
136,863

 
166,163
Tolling arrangements
GWh
102,819

 
104,154
Fair Value of Derivative Instruments
The following table summarizes the gross and net fair values of commodity derivative instruments at June 30, 2012:
 
 
Derivative Assets
 
Derivative Liabilities
 
 
(in millions)
 
Short-Term
 
Long-Term
 
Subtotal
 
Short-Term
 
Long-Term
 
Subtotal
 
Net
Liability
Non-trading activities
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Economic hedges
 
$
69

 
$
75

 
$
144

 
$
245

 
$
830

 
$
1,075

 
$
931

Netting and collateral
 
(24
)
 
(16
)
 
(40
)
 
(72
)
 
(34
)
 
(106
)
 
(66
)
Total
 
$
45

 
$
59

 
$
104

 
$
173

 
$
796

 
$
969

 
$
865

The following table summarizes the gross and net fair values of commodity derivative instruments at December 31, 2011:
 
 
Derivative Assets
 
Derivative Liabilities
 
 
(in millions)
 
Short-Term
 
Long-Term
 
Subtotal
 
Short-Term
 
Long-Term
 
Subtotal
 
Net
Liability
Non-trading activities
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Economic hedges
 
$
86

 
$
85

 
$
171

 
$
303

 
$
856

 
$
1,159

 
$
988

Netting and collateral
 
(21
)
 
(15
)
 
(36
)
 
(37
)
 
(51
)
 
(88
)
 
(52
)
Total
 
$
65

 
$
70

 
$
135

 
$
266

 
$
805

 
$
1,071

 
$
936
Summarization of Economic Hedging Activities
The following table summarizes the components of economic hedging activity:
 
Three months ended
June 30,
 
Six months ended
June 30,
(in millions)
2012
 
2011
 
2012
 
2011
Realized gains (losses)
$
(67
)
 
$
(35
)
 
$
(122
)
 
$
(74
)
Unrealized gains (losses)
423

 
(227
)
 
62

 
(323
)
Summary of Margin and Collateral Deposits Provided to and Received from Counterparties
The following table summarizes margin and collateral deposits provided to counterparties:
(in millions)
June 30,
2012
 
December 31, 2011
Collateral provided to counterparties:
 
 
 
Offset against derivative liabilities
$
66

 
$
51

Reflected in other current assets
25

 
17