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Segment Information Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Generation Mid Atlantic [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | $ 3,073 | $ 3,214 | $ 3,317
Generation Midwest [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 3,135 | 2,820 | 2,971
Generation New England [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 354 | 514 | 438
Generation New York [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 1,122 | 1,008 | 752
Generation ERCOT [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 258 | 332 | 281
Generation Other Regions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 375 | 305 | 336
Generation Reportable Segments Total [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 8,317 | 8,193 | 8,095
Generation All Other Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel | [1] | 427 | 617 | 832
Unrealized Gain (Loss) on Securities |  | (262) | (131) | (500)
Generation Total Consolidated Group [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue Net of Purchase Power And Fuel |  | 8,744 | 8,810 | 8,927
Operating Segments [Member] | Generation Mid Atlantic [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 3,022 | 3,105 | 3,282
Operating Segments [Member] | Generation Midwest [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 3,112 | 2,810 | 2,969
Operating Segments [Member] | Generation New England [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 368 | 538 | 467
Operating Segments [Member] | Generation New York [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 1,112 | 1,007 | 771
Operating Segments [Member] | Generation ERCOT [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 501 | 575 | 412
Operating Segments [Member] | Generation Other Regions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 515 | 476 | 483
Operating Segments [Member] | Generation Reportable Segments Total [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 8,630 | 8,511 | 8,384
Operating Segments [Member] | Generation All Other Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [1],[2] | 114 | 299 | 543
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel |  |  | 54 | 57
Unrealized Gain (Loss) on Securities |  | (319) | (175) | (41)
Nuclear Fuel Amortization |  | (57) | (12) | (60)
Operating Segments [Member] | Generation Total Consolidated Group [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
RNF from external customers | [2] | 8,744 | 8,810 | 8,927
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | 51 | 109 | 35
Intersegment Eliminations [Member] | Generation Midwest [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | 23 | 10 | 2
Intersegment Eliminations [Member] | Generation New England [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | (14) | (24) | (29)
Intersegment Eliminations [Member] | Generation New York [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | 10 | 1 | (19)
Intersegment Eliminations [Member] | Generation ERCOT [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | (243) | (243) | (131)
Intersegment Eliminations [Member] | Generation Other Regions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | (140) | (171) | (147)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | (313) | (318) | (289)
Intersegment Eliminations [Member] | Generation All Other Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel | [1] | 313 | 318 | 289
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment Revenue Net Of Purchase Power And Fuel |  | $ 0 | $ 0 | $ 0
[1] | Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million and $57 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 and 2016, respectively, unrealized mark-to-market losses of $319 million, $175 million, and $41 million in 2018, 2017, and 2016, respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $57 million, $12 million and $60 million for the year ended December 31, 2018, 2017, and 2016 and the elimination of intersegment RNF.
[2] | Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants.

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