| Segment and Significant Customer Information |
Segment Information We assess our business on a regional basis due to the impact on our financial performance of the differing characteristics of these regions, particularly with respect to competition, regulation and other factors impacting supply and demand. At March 31, 2012, our reportable segments were West (including geothermal), Texas, North (including Canada) and Southeast. We continue to evaluate the optimal manner in which we assess our performance including our segments and future changes may result. Commodity Margin includes our power and steam revenues, sales of purchased power and physical natural gas, capacity revenue, REC revenue, sales of surplus emission allowances, transmission revenue and expenses, fuel and purchased energy expense, fuel transportation expense, RGGI compliance and other environmental costs, and cash settlements from our marketing, hedging and optimization activities including natural gas transactions hedging future power sales that are included in mark-to-market activity, but excludes the unrealized portion of our mark-to-market activity and other revenues. Commodity Margin is a key operational measure reviewed by our chief operating decision maker to assess the performance of our segments. The tables below show our financial data for our segments for the periods indicated (in millions). | | | | | | | | | | | | | | | | | | | | | | | | | | Three Months Ended March 31, 2012 | | West | | Texas | | North | | Southeast | | Consolidation and Elimination | | Total | Revenues from external customers | $ | 416 |
| | $ | 356 |
| | $ | 298 |
| | $ | 166 |
| | $ | — |
| | $ | 1,236 |
| Intersegment revenues | 4 |
| | 20 |
| | 3 |
| | 22 |
| | (49 | ) | | — |
| Total operating revenues | $ | 420 |
| | $ | 376 |
| | $ | 301 |
| | $ | 188 |
| | $ | (49 | ) | | $ | 1,236 |
| Commodity Margin | $ | 208 |
| | $ | 109 |
| | $ | 144 |
| | $ | 56 |
| | $ | — |
| | $ | 517 |
| Add: Mark-to-market commodity activity, net and other(1)(2) | 36 |
| | 34 |
| | 12 |
| | 10 |
| | (8 | ) | | 84 |
| Less: | | | | | | | | | | | | Plant operating expense | 81 |
| | 68 |
| | 45 |
| | 33 |
| | (6 | ) | | 221 |
| Depreciation and amortization expense | 50 |
| | 35 |
| | 33 |
| | 23 |
| | (1 | ) | | 140 |
| Sales, general and other administrative expense | 8 |
| | 11 |
| | 6 |
| | 8 |
| | — |
| | 33 |
| Other operating expenses(3) | 11 |
| | 2 |
| | 9 |
| | 1 |
| | (2 | ) | | 21 |
| (Income) from unconsolidated investments in power plants | — |
| | — |
| | (9 | ) | | — |
| | — |
| | (9 | ) | Income from operations | 94 |
| | 27 |
| | 72 |
| | 1 |
| | 1 |
| | 195 |
| Interest expense, net of interest income | | | | | | | | | | | 182 |
| Loss on interest rate derivatives | | | | | | | | | | | 14 |
| Debt extinguishment costs and other (income) expense, net | | | | | | | | | | | 14 |
| Loss before income taxes | | | | | | | | | | | $ | (15 | ) |
| | | | | | | | | | | | | | | | | | | | | | | | | | Three Months Ended March 31, 2011 | | West | | Texas | | North | | Southeast | | Consolidation and Elimination | | Total | Revenues from external customers | $ | 599 |
| | $ | 450 |
| | $ | 271 |
| | $ | 179 |
| | $ | — |
| | $ | 1,499 |
| Intersegment revenues | 3 |
| | 5 |
| | 8 |
| | 45 |
| | (61 | ) | | — |
| Total operating revenues | $ | 602 |
| | $ | 455 |
| | $ | 279 |
| | $ | 224 |
| | $ | (61 | ) | | $ | 1,499 |
| Commodity Margin | $ | 233 |
| | $ | 67 |
| | $ | 135 |
| | $ | 54 |
| | $ | — |
| | $ | 489 |
| Add: Mark-to-market commodity activity, net and other(1) | 5 |
| | (60 | ) | | 4 |
| | (4 | ) | | (6 | ) | | (61 | ) | Less: | | | | | | | | | | | | Plant operating expense | 87 |
| | 80 |
| | 45 |
| | 33 |
| | (7 | ) | | 238 |
| Depreciation and amortization expense | 46 |
| | 30 |
| | 33 |
| | 23 |
| | (1 | ) | | 131 |
| Sales, general and other administrative expense | 11 |
| | 10 |
| | 6 |
| | 5 |
| | — |
| | 32 |
| Other operating expenses(3) | 8 |
| | — |
| | 7 |
| | 1 |
| | 2 |
| | 18 |
| (Income) from unconsolidated investments in power plants | — |
| | — |
| | (9 | ) | | — |
| | — |
| | (9 | ) | Income (loss) from operations | 86 |
| | (113 | ) | | 57 |
| | (12 | ) | | — |
| | 18 |
| Interest expense, net of interest income | | | | | | | | | | | 188 |
| Loss on interest rate derivatives | | | | | | | | | | | 109 |
| Debt extinguishment costs and other (income) expense, net | | | | | | | | | | | 100 |
| Loss before income taxes | | | | | | | | | | | $ | (379 | ) |
__________ | | (1) | Mark-to-market commodity activity represents the change in the unrealized portion of our mark-to-market activity, net, included in operating revenues and fuel and purchased energy expense on our Consolidated Condensed Statements of Operations for the three months ended March 31, 2012 and 2011. |
| | (2) | Includes $(8) million of lease levelization and $4 million of amortization expense for the three months ended March 31, 2012 related to contracts that became effective in June and August 2011. |
| | (3) | Excludes $3 million and $2 million of RGGI compliance and other environmental costs for the three months ended March 31, 2012 and 2011, respectively, which are components of Commodity Margin. |
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