v2.4.0.6
Segment and Significant Customer Information (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenues from external customers $ 1,996 $ 2,209 $ 4,111 $ 5,341
Intersegment revenues 0 0 0 0
Total operating revenues 1,996 2,209 4,111 5,341
Commodity Margin 897 825 2,023 1,921
Add: Mark-to-market commodity activity, net and other 202 [1],[2] (20) [1],[2] (58) [1],[3] (57) [1],[3]
Plant operating expense 207 212 699 711
Depreciation and amortization expense 140 143 418 405
Sales, general and other administrative expense 36 33 104 99
Other operating expenses 18 [4] 19 [4] 58 [4] 57 [4]
(Income) loss from unconsolidated investments in power plants (7) (5) (21) (12)
Income (loss) from operations 705 403 707 604
Interest expense, net of interest income 181 190 545 568
Loss on interest rate derivatives 0 3 14 149
Debt Extinguishment Costs and Other (Income) Expense, Net 6 0 26 108
Income (loss) before income taxes and discontinued operations 518 210 122 (221)
Lease levelization 16 11 7 15
Contract amortization 4 4 11 5
RGGI Compliance and Other Environmental Costs 4 3 9 7
Commodity Margin Riverside Energy Center 32 31 64 62
West [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenues from external customers 509 688 1,183 1,753
Intersegment revenues 2 3 7 7
Total operating revenues 511 691 1,190 1,760
Commodity Margin 330 329 748 798
Add: Mark-to-market commodity activity, net and other (40) [1],[2] 20 [1],[2] (80) [1],[3] 36 [1],[3]
Plant operating expense 88 94 281 297
Depreciation and amortization expense 52 52 151 140
Sales, general and other administrative expense 9 10 23 29
Other operating expenses 10 [4] 11 [4] 30 [4] 30 [4]
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income (loss) from operations 131 182 183 338
Texas [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenues from external customers 886 843 1,430 1,939
Intersegment revenues (34) 3 27 13
Total operating revenues 852 846 1,457 1,952
Commodity Margin 218 162 472 357
Add: Mark-to-market commodity activity, net and other 249 [1],[2] (21) [1],[2] 66 [1],[3] (54) [1],[3]
Plant operating expense 49 50 189 193
Depreciation and amortization expense 35 34 104 99
Sales, general and other administrative expense 12 10 36 33
Other operating expenses 1 [4] (1) [4] 4 [4] 2 [4]
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income (loss) from operations 370 48 205 (24)
North [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenues from external customers 407 430 974 1,025
Intersegment revenues 4 (8) 9 5
Total operating revenues 411 422 983 1,030
Commodity Margin 266 [5] 259 [5] 591 [5] 578 [5]
Add: Mark-to-market commodity activity, net and other (26) [1],[2] (11) [1],[2] (17) [1],[3] (12) [1],[3]
Plant operating expense 51 44 154 136
Depreciation and amortization expense 33 36 100 102
Sales, general and other administrative expense 8 7 22 19
Other operating expenses 6 [4] 7 [4] 21 [4] 23 [4]
(Income) loss from unconsolidated investments in power plants (7) (5) (21) (12)
Income (loss) from operations 149 159 298 298
Southeast [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenues from external customers 194 248 524 624
Intersegment revenues 68 31 84 116
Total operating revenues 262 279 608 740
Commodity Margin 83 75 212 188
Add: Mark-to-market commodity activity, net and other 27 [1],[2] 0 [1],[2] (5) [1],[3] (4) [1],[3]
Plant operating expense 29 33 98 107
Depreciation and amortization expense 21 22 66 67
Sales, general and other administrative expense 8 7 23 18
Other operating expenses (1) [4] 0 [4] 2 [4] 3 [4]
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income (loss) from operations 53 13 18 (11)
Consolidation and Elimination [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenues from external customers 0 0 0 0
Intersegment revenues (40) (29) (127) (141)
Total operating revenues (40) (29) (127) (141)
Commodity Margin 0 0 0 0
Add: Mark-to-market commodity activity, net and other (8) [1],[2] (8) [1],[2] (22) [1],[3] (23) [1],[3]
Plant operating expense (10) (9) (23) (22)
Depreciation and amortization expense (1) (1) (3) (3)
Sales, general and other administrative expense (1) (1) 0 0
Other operating expenses 2 [4] 2 [4] 1 [4] (1) [4]
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income (loss) from operations $ 2 $ 1 $ 3 $ 3
[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
[2] Includes $16 million and $11 million of lease levelization for the three months ended September 30, 2012 and 2011, respectively, and $4 million of amortization expense for each of the three months ended September 30, 2012 and 2011.
[3] Includes $7 million and $15 million of lease levelization and $11 million and $5 million of amortization expense for the nine months ended September 30, 2012 and 2011, respectively.
[4] Excludes $4 million and $3 million of RGGI compliance and other environmental costs for the three months ended September 30, 2012 and 2011, respectively, and $9 million and $7 million for the nine months ended September 30, 2012 and 2011, respectively, which are components of Commodity Margin.
[5] Our North segment includes Commodity Margin related to Riverside Energy Center, LLC of $32 million and $31 million for the three months ended September 30, 2012 and 2011, respectively, and $64 million and $62 million for the nine months ended September 30, 2012 and 2011, respectively.