v3.6.0.2
Segment and Significant Customer Information (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Sep. 30, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues $ 1,582 $ 2,355 $ 1,164 $ 1,615 $ 1,436 $ 1,948 $ 1,442 $ 1,646   $ 6,716 $ 6,472 $ 8,030
Commodity Margin                   2,604 2,786 2,759 [1]
Mark-to-Market Commodity Activity, Net and Other Revenue [2]                   (75) (81) 379
Plant operating expense                   977 1,018 969
Depreciation and amortization expense                   662 638 603
Sales, general and other administrative expense                   140 138 144
Other Cost and Expense, Operating                   79 80 88
Impairment losses                   13 0 123
(Gain) on sale of assets, net                   (157) 0 (753)
(Income) from unconsolidated subsidiaries                   (24) (24) (25)
Income from operations $ 234 [3] $ 462 [3] $ 140 [3] $ 3 [3] $ 22 $ 466 $ 201 $ 166   839 855 1,989
Interest expense, net of interest income                   631 628 645
Debt Extinguishment Costs and Other (Income) Expense, Net                   49 54 361
Income before income taxes                   159 173 983
Lease levelization                   (2) (2) (5)
Contract amortization                   $ 218 $ 91 $ 20
Number of significant customers                   0 two one
West [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   $ 1,569 $ 2,094 $ 2,358
Commodity Margin                   991 1,106 1,050 [1]
Mark-to-Market Commodity Activity, Net and Other Revenue [2]                   (3) 160 220
Plant operating expense                   357 416 385
Depreciation and amortization expense                   225 250 245
Sales, general and other administrative expense                   39 35 41
Other Cost and Expense, Operating                   32 37 50
Impairment losses                   13   0
(Gain) on sale of assets, net                   0   0
(Income) from unconsolidated subsidiaries                   0 0 0
Income from operations                   322 528 549
Texas [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   2,815 2,359 3,252
Commodity Margin                   655 736 760 [1]
Mark-to-Market Commodity Activity, Net and Other Revenue [2]                   (23) (120) 142
Plant operating expense                   317 338 313
Depreciation and amortization expense                   213 204 191
Sales, general and other administrative expense                   56 63 64
Other Cost and Expense, Operating                   9 9 5
Impairment losses                   0   0
(Gain) on sale of assets, net                   0   0
(Income) from unconsolidated subsidiaries                   0 0 0
Income from operations                   37 2 329
East [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   2,364 2,047 2,496
Commodity Margin                   958 944 949 [1]
Mark-to-Market Commodity Activity, Net and Other Revenue [2]                   (20) (92) 48
Plant operating expense                   332 292 302
Depreciation and amortization expense                   224 184 168
Sales, general and other administrative expense                   45 40 39
Other Cost and Expense, Operating                   38 36 32
Impairment losses                   0   123
(Gain) on sale of assets, net                   (157)   (753)
(Income) from unconsolidated subsidiaries                   (24) (24) (25)
Income from operations                   480 324 1,111
Commodity Margin for Six Southeast Power Plants Sold                       81
Number of power plants disposed of                 6      
Geography Consolidation and Elimination [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   (32) (28) (76)
Commodity Margin                   0 0 0
Mark-to-Market Commodity Activity, Net and Other Revenue                   (29) (29) (31)
Plant operating expense                   (29) (28) (31)
Depreciation and amortization expense                   0 0 (1)
Sales, general and other administrative expense                   0 0 0
Other Cost and Expense, Operating                   0 (2) 1
Impairment losses                   0   0
(Gain) on sale of assets, net                   0   0
(Income) from unconsolidated subsidiaries                   0 0 0
Income from operations                   0 1 0
PJM Settlement, Inc. [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                     724 1,000
Pacific Gas & Electric Company [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                     642  
Operating Segments [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   6,716 6,472 8,030
Operating Segments [Member] | West [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   1,562 2,089 2,352
Operating Segments [Member] | Texas [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   2,801 2,344 3,229
Operating Segments [Member] | East [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   2,353 2,039 2,449
Operating Segments [Member] | Geography Consolidation and Elimination [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   0 0 0
Intersegment Eliminations [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   0 0 0
Intersegment Eliminations [Member] | West [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   7 5 6
Intersegment Eliminations [Member] | Texas [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   14 15 23
Intersegment Eliminations [Member] | East [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   11 8 47
Intersegment Eliminations [Member] | Geography Consolidation and Elimination [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Operating revenues                   (32) (28) (76)
Other Assets [Member]                        
Revenues from External Customers and Long-Lived Assets [Line Items]                        
Contract amortization                   $ 122 $ 20 $ 14
[1] Our East segment includes Commodity Margin of $81 million for the year ended December 31, 2014 related to the six power plants in our East segment that were sold in July 2014.
[2] Includes $(2) million, $(2) million and $(5) million of lease levelization and $122 million, $20 million and $14 million of amortization expense for the years ended December 31, 2016, 2015 and 2014, respectively.
[3] We recorded a gain on sale of assets, net of $(157) million in connection with the sale of the Mankato Power Plant which is included in income from operations on our Consolidated Statement of Operations for the year ended December 31, 2016.