v3.4.0.3
Segment Information (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues $ 1,615 $ 1,646
Commodity Margin 580 535
Add: Mark-to-market commodity activity, net and other [1] (91) 101
Plant operating expense 255 260
Depreciation and amortization expense 180 158
Sales, general and other administrative expense 38 37
Other operating expenses 20 20
(Income) loss from unconsolidated investments in power plants (7) (5)
Income from operations 3 166
Interest expense, net of interest income 156 153
Other (income) expense, net 6 2
Debt Extinguishment Costs and Other (Income) Expense, Net   21
Loss before income taxes (159) (8)
Lease levelization (22) (24)
Amortization of Intangible Assets 27 4
West [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 426 517
Commodity Margin 197 218
Add: Mark-to-market commodity activity, net and other [1] 46 119
Plant operating expense 91 106
Depreciation and amortization expense 69 67
Sales, general and other administrative expense 10 10
Other operating expenses 8 10
(Income) loss from unconsolidated investments in power plants 0 0
Income from operations 65 144
Texas [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 535 584
Commodity Margin 153 149
Add: Mark-to-market commodity activity, net and other [1] (110) 41
Plant operating expense 86 89
Depreciation and amortization expense 53 49
Sales, general and other administrative expense 16 17
Other operating expenses 2 2
(Income) loss from unconsolidated investments in power plants 0 0
Income from operations (114) 33
East [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 662 552
Commodity Margin 230 168
Add: Mark-to-market commodity activity, net and other [1] (21) (52)
Plant operating expense 84 72
Depreciation and amortization expense 58 42
Sales, general and other administrative expense 12 10
Other operating expenses 10 8
(Income) loss from unconsolidated investments in power plants (7) (5)
Income from operations 52 (11)
Consolidation, Eliminations [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues (8) (7)
Commodity Margin 0 0
Add: Mark-to-market commodity activity, net and other [1] (6) (7)
Plant operating expense (6) (7)
Depreciation and amortization expense 0 0
Sales, general and other administrative expense 0 0
Other operating expenses 0 0
(Income) loss from unconsolidated investments in power plants 0 0
Income from operations 0 0
Operating Segments [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 1,615 1,646
Operating Segments [Member] | West [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 424 515
Operating Segments [Member] | Texas [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 532 581
Operating Segments [Member] | East [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 659 550
Operating Segments [Member] | Consolidation, Eliminations [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 0 0
Intersegment Eliminations [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 0 0
Intersegment Eliminations [Member] | West [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 2 2
Intersegment Eliminations [Member] | Texas [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 3 3
Intersegment Eliminations [Member] | East [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues 3 2
Intersegment Eliminations [Member] | Consolidation, Eliminations [Member]    
Revenues from External Customers and Long-Lived Assets [Line Items]    
Operating revenues $ (8) $ (7)
[1] Includes $(22) million and $(24) million of lease levelization and $27 million and $4 million of amortization expense for the three months ended March 31, 2016 and 2015, respectively.