v2.4.0.6
Segment and Significant Customer Information (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenues from external customers $ 1,236 $ 1,499
Intersegment revenues 0 0
Total operating revenues 1,236 1,499
Commodity Margin 517 489
Add: Mark-to-market commodity activity, net and other 84 [1],[2] (61) [1]
Plant operating expense 221 238
Depreciation and amortization expense 140 131
Sales, general and other administrative expense 33 32
Other operating expenses 21 [3] 18 [3]
(Income) from unconsolidated investments in power plants (9) (9)
Income from operations 195 18
Interest expense, net of interest income 182 188
Loss on interest rate derivatives 14 109
Debt extinguishment costs and other (income) expense, net 14 100
Income (loss) before income taxes and discontinued operations (15) (379)
Lease levelization (8)  
Contract amortization 4  
RGGI compliance and other environmental costs 3 2
West [Member]
    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenues from external customers 416 599
Intersegment revenues 4 3
Total operating revenues 420 602
Commodity Margin 208 233
Add: Mark-to-market commodity activity, net and other 36 [1],[2] 5 [1]
Plant operating expense 81 87
Depreciation and amortization expense 50 46
Sales, general and other administrative expense 8 11
Other operating expenses 11 [3] 8 [3]
(Income) from unconsolidated investments in power plants 0 0
Income from operations 94 86
Texas [Member]
    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenues from external customers 356 450
Intersegment revenues 20 5
Total operating revenues 376 455
Commodity Margin 109 67
Add: Mark-to-market commodity activity, net and other 34 [1],[2] (60) [1]
Plant operating expense 68 80
Depreciation and amortization expense 35 30
Sales, general and other administrative expense 11 10
Other operating expenses 2 [3] 0 [3]
(Income) from unconsolidated investments in power plants 0 0
Income from operations 27 (113)
North [Member]
    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenues from external customers 298 271
Intersegment revenues 3 8
Total operating revenues 301 279
Commodity Margin 144 135
Add: Mark-to-market commodity activity, net and other 12 [1],[2] 4 [1]
Plant operating expense 45 45
Depreciation and amortization expense 33 33
Sales, general and other administrative expense 6 6
Other operating expenses 9 [3] 7 [3]
(Income) from unconsolidated investments in power plants (9) (9)
Income from operations 72 57
Southeast [Member]
    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenues from external customers 166 179
Intersegment revenues 22 45
Total operating revenues 188 224
Commodity Margin 56 54
Add: Mark-to-market commodity activity, net and other 10 [1],[2] (4) [1]
Plant operating expense 33 33
Depreciation and amortization expense 23 23
Sales, general and other administrative expense 8 5
Other operating expenses 1 [3] 1 [3]
(Income) from unconsolidated investments in power plants 0 0
Income from operations 1 (12)
Consolidation and Elimination [Member]
    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Revenues from external customers 0 0
Intersegment revenues (49) (61)
Total operating revenues (49) (61)
Commodity Margin 0 0
Add: Mark-to-market commodity activity, net and other (8) [1],[2] (6) [1]
Plant operating expense (6) (7)
Depreciation and amortization expense (1) (1)
Sales, general and other administrative expense 0 0
Other operating expenses (2) [3] 2 [3]
(Income) from unconsolidated investments in power plants 0 0
Income from operations $ 1 $ 0
[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.