v2.4.0.8
Segment and Significant Customer Information (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue from External Customer $ 2,050 $ 1,996 $ 4,863 $ 4,111
Intersegment revenue 0 0 0 0
Operating revenues 2,050 1,996 4,863 4,111
Commodity Margin 985 897 [1],[2] 1,979 2,023 [1],[2]
Add: Mark-to-market commodity activity, net and other 6 [3] 202 [3] 4 [4] (58) [4]
Plant operating expense 200 207 684 699
Depreciation and amortization expense 150 140 441 418
Sales, general and other administrative expense 33 36 102 104
Other operating expenses 20 18 58 58
(Income) loss from unconsolidated investments in power plants (9) (7) (25) (21)
Income from operations 597 705 723 707
Interest expense, net of interest income 174 181 517 545
Loss on interest rate derivatives 0 0 0 14
Debt Extinguishment Costs and Other (Income) Expense, Net     83 26
Debt Extinguishment Costs and Other (Income) Expense, Net 7 6 15 14
Income before income taxes 416 518 123 122
Lease levelization 44 16 17 7
Commodity Margin Riverside Energy Center   32   64
Commodity Margin Broad River Energy Center   20   44
Contract amortization 4 4 11 11
West [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue from External Customer 620 509 1,482 1,183
Intersegment revenue 1 2 2 7
Operating revenues 621 511 1,484 1,190
Commodity Margin 337 330 [1],[2] 737 748 [1],[2]
Add: Mark-to-market commodity activity, net and other 16 [3] (40) [3] (2) [4] (80) [4]
Plant operating expense 80 88 261 281
Depreciation and amortization expense 57 52 160 151
Sales, general and other administrative expense 4 9 11 23
Other operating expenses 11 10 31 30
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income from operations 201 131 272 183
Texas [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue from External Customer 842 886 1,820 1,430
Intersegment revenue (6) (34) (24) 27
Operating revenues 836 852 1,796 1,457
Commodity Margin 328 218 [1],[2] 537 472 [1],[2]
Add: Mark-to-market commodity activity, net and other (5) [3] 249 [3] 18 [4] 66 [4]
Plant operating expense 60 49 224 189
Depreciation and amortization expense 42 35 129 104
Sales, general and other administrative expense 17 12 55 36
Other operating expenses 2 1 4 4
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income from operations 202 370 143 205
North [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue from External Customer 401 407 1,055 974
Intersegment revenue 12 4 27 9
Operating revenues 413 411 1,082 983
Commodity Margin 242 266 [1],[2] 543 591 [1],[2]
Add: Mark-to-market commodity activity, net and other (3) [3] (26) [3] (8) [4] (17) [4]
Plant operating expense 40 51 130 154
Depreciation and amortization expense 33 33 98 100
Sales, general and other administrative expense 6 8 18 22
Other operating expenses 9 6 23 21
(Income) loss from unconsolidated investments in power plants (9) (7) (25) (21)
Income from operations 160 149 291 298
Southeast [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue from External Customer 187 194 506 524
Intersegment revenue 57 68 161 84
Operating revenues 244 262 667 608
Commodity Margin 78 83 [1],[2] 162 212 [1],[2]
Add: Mark-to-market commodity activity, net and other 6 [3] 27 [3] 20 [4] (5) [4]
Plant operating expense 27 29 92 98
Depreciation and amortization expense 18 21 55 66
Sales, general and other administrative expense 5 8 17 23
Other operating expenses 1 (1) 2 2
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income from operations 33 53 16 18
Consolidation and Elimination [Member]
        
Revenues from External Customers and Long-Lived Assets [Line Items]        
Revenue from External Customer 0 0 0 0
Intersegment revenue (64) (40) (166) (127)
Operating revenues (64) (40) (166) (127)
Commodity Margin 0 0 [1],[2] 0 0 [1],[2]
Add: Mark-to-market commodity activity, net and other (8) [3] (8) [3] (24) [4] (22) [4]
Plant operating expense (7) (10) (23) (23)
Depreciation and amortization expense 0 (1) (1) (3)
Sales, general and other administrative expense 1 (1) 1 0
Other operating expenses (3) 2 (2) 1
(Income) loss from unconsolidated investments in power plants 0 0 0 0
Income from operations $ 1 $ 2 $ 1 $ 3
[1] Our North segment includes Commodity Margin of $32 million and $64 million for the three and nine months ended September 30, 2012 related to Riverside Energy Center, LLC, which was sold in December 2012.
[2] Our Southeast segment includes Commodity Margin of $20 million and $44 million for the three and nine months ended September 30, 2012 related to Broad River, which was sold in December 2012.
[3] Includes $44 million and $16 million of lease levelization and $4 million and $4 million of amortization expense for the three months ended September 30, 2013 and 2012, respectively
[4] Includes $17 million and $7 million of lease levelization and $11 million and $11 million of amortization expense for the nine months ended September 30, 2013 and 2012, respectively.