v2.4.0.6

Use of Collateral (Tables) | 12 Months Ended
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Dec. 31, 2012
Use of Collateral [Abstract] |
Schedule of Collateral | The table below summarizes the balances outstanding under margin deposits, natural gas and power prepayments, and exposure under letters of credit and first priority liens for commodity procurement and risk management activities as of December 31, 2012 and 2011 (in millions):
| 2012 |  | 2011
Margin deposits(1) | $ | 196 |  |  | $ | 140 |
Natural gas and power prepayments | 35 |  |  | 42 |
Total margin deposits and natural gas and power prepayments with our counterparties(2) | $ | 231 |  |  | $ | 182 |
Letters of credit issued | $ | 484 |  |  | $ | 581 |
First priority liens under power and natural gas agreements | 14 |  |  | 1 |
First priority liens under interest rate swap agreements | 206 |  |  | 318 |
Total letters of credit and first priority liens with our counterparties | $ | 704 |  |  | $ | 900 |
Margin deposits held by us posted by our counterparties(1)(3) | $ | 11 |  |  | $ | 34 |
Letters of credit posted with us by our counterparties | 1 |  |  | — |
Total margin deposits and letters of credit posted with us by our counterparties | $ | 12 |  |  | $ | 34 |
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(1) | Balances are subject to master netting arrangements and presented on a gross basis on our Consolidated Balance Sheets. We do not offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation.
(2) | At December 31, 2012 and 2011, $211 million and $162 million, respectively, were included in margin deposits and other prepaid expense and $20 million and $20 million, respectively, were included in other assets on our Consolidated Balance Sheets.
(3) | Included in other current liabilities on our Consolidated Balance Sheets.

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