v2.4.0.8

Derivative Instruments (Detail 5) (Details) (USD $) In Millions, unless otherwise specified | Jun. 30, 2013 | Dec. 31, 2012
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Derivative Instruments Subject to Master Netting Arrangement [Line Items] |  |  |  |
Derivative, Fair Value, Gross Amount Not Offset Against Collateral, Net | $ (184) |  | $ (213) |
Derivative Fair Value, Amount Not Offset Against Collateral, Net | 0 |  | 0 |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 32 |  | 34 |
Derivative Asset, Fair Value, Gross Asset | 737 |  | 437 |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | (687) |  | (396) |
Derivative Liability, Fair Value, Gross Liability | (921) |  | (650) |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 687 |  | 396 |
Margin/Cash (Received) Posted Subject to Master Netting Arrangement | 59 | [1] | 39 | [1]
Derivative Liability, Fair Value, Amount Offset Against Collateral | (157) |  | (208) |
Derivative, Fair Value, Amount Offset Against Collateral, Net | (125) |  | (174) |
Derivative, Collateral, Right to Reclaim Cash | 77 | [1] | 46 | [1]
Derivative, Collateral, Obligation to Return Cash | (18) | [1] | (7) | [1]
Commodity Exchange Traded Futures and Swaps Contracts [Member] |  |  |  |
Derivative Instruments Subject to Master Netting Arrangement [Line Items] |  |  |  |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 0 |  | 0 |
Derivative Asset, Fair Value, Gross Asset | 595 |  | 385 |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | (580) |  | (379) |
Derivative Liability, Fair Value, Gross Liability | (646) |  | (424) |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 580 |  | 379 |
Derivative Liability, Fair Value, Amount Offset Against Collateral | 0 |  | 0 |
Derivative, Collateral, Right to Reclaim Cash | 66 | [1] | 45 | [1]
Derivative, Collateral, Obligation to Return Cash | (15) | [1] | (6) | [1]
Commodity Forward Contract [Member] |  |  |  |
Derivative Instruments Subject to Master Netting Arrangement [Line Items] |  |  |  |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 24 |  | 30 |
Derivative Asset, Fair Value, Gross Asset | 134 |  | 48 |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | (107) |  | (17) |
Derivative Liability, Fair Value, Gross Liability | (130) |  | (26) |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 107 |  | 17 |
Derivative Liability, Fair Value, Amount Offset Against Collateral | (12) |  | (8) |
Derivative, Collateral, Right to Reclaim Cash | 11 | [1] | 1 | [1]
Derivative, Collateral, Obligation to Return Cash | (3) | [1] | (1) | [1]
Interest Rate Swap [Member] |  |  |  |
Derivative Instruments Subject to Master Netting Arrangement [Line Items] |  |  |  |
Derivative, Fair Value, Gross Amount Not Offset Against Collateral, Net | (137) |  | (196) |
Derivative Asset, Fair Value, Amount Offset Against Collateral | 8 |  | 4 |
Derivative Asset, Fair Value, Gross Asset | 8 |  | 4 |
Derivative Asset, Fair Value, Amount Not Offset Against Collateral | 0 |  | 0 |
Derivative Liability, Fair Value, Gross Liability | (145) |  | (200) |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 0 |  | 0 |
Derivative Liability, Fair Value, Amount Offset Against Collateral | (145) |  | (200) |
Derivative, Collateral, Right to Reclaim Cash | 0 | [1] | 0 | [1]
Derivative, Collateral, Obligation to Return Cash | $ 0 | [1] | $ 0 | [1]
[1] | Negative balances represent margin deposits posted with us by our counterparties related to our derivative activities that are subject to a master netting arrangement. Positive balances reflect margin deposits and natural gas and power prepayments posted by us with our counterparties related to our derivative activities that are subject to a master netting arrangement. See Note 6 for a further discussion of our collateral.

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- Definition Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226016-175313 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959 + Details
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