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Segment Information Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  | $ 8,814 | $ 9,403 | $ 8,076 | $ 9,693 | $ 8,384 | $ 8,768 | $ 7,665 | $ 8,747 | $ 35,985 | $ 33,565 | $ 31,366
Revenue from Related Parties |  |  |  |  |  |  |  |  |  |  | 0 | 0
Generation Mid Atlantic [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 5,487 | 5,540 | 6,179
Generation Midwest [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 4,706 | 4,181 | 4,412
Generation New England [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 2,841 | 2,002 | 1,769
Generation New York [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 1,687 | 1,550 | 1,166
Generation ERCOT [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 1,133 | 962 | 837
Generation Other Regions [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 1,494 | 1,049 | 907
Generation Reportable Segments Total [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 17,348 | 15,284 | 15,270
Generation Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 2,780 | 2,628 | 2,281
Generation All Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [1] |  |  |  |  |  |  |  |  | 309 | 588 | 206
Unrealized Gain (Loss) on Securities |  |  |  |  |  |  |  |  |  | (262) | (131) | (500)
Generation Total Consolidated Group [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  |  | 20,437 | 18,500 | 17,757
Operating Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [2] |  |  |  |  |  |  |  |  | 35,985 | 33,567 | 31,365
Operating Segments [Member] | Generation Mid Atlantic [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 5,474 | 5,515 | 6,212
Operating Segments [Member] | Generation Midwest [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 4,717 | 4,206 | 4,402
Operating Segments [Member] | Generation New England [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 2,845 | 2,010 | 1,778
Operating Segments [Member] | Generation New York [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 1,687 | 1,567 | 1,208
Operating Segments [Member] | Generation ERCOT [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 1,132 | 958 | 831
Operating Segments [Member] | Generation Other Regions [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 1,556 | 1,076 | 969
Operating Segments [Member] | Generation Reportable Segments Total [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 17,411 | 15,332 | 15,400
Operating Segments [Member] | Generation Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 2,718 | 2,575 | 2,146
Operating Segments [Member] | Generation All Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Amortization of intangible assets related to commodity contracts |  |  |  |  |  |  |  |  |  |  | (38) | 52
Unrealized Gain (Loss) on Securities |  |  |  |  |  |  |  |  |  | (319) | (175) | (41)
Operating Segments [Member] | Generation Total Consolidated Group [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 20,437 | 18,500 | 17,757
Corporate, Non-Segment [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | (1) | 7 | 10
Corporate, Non-Segment [Member] | Generation All Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [1],[3] |  |  |  |  |  |  |  |  | 308 | 593 | 211
Intersegment Eliminations [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [2] |  |  |  |  |  |  |  |  | (3,294) | (3,025) | (3,164)
Revenue from Related Parties | [4] |  |  |  |  |  |  |  |  | 1 | 2 | 5
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | 13 | 25 | (33)
Intersegment Eliminations [Member] | Generation Midwest [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | (11) | (25) | 10
Intersegment Eliminations [Member] | Generation New England [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | (4) | (8) | (9)
Intersegment Eliminations [Member] | Generation New York [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | 0 | (17) | (42)
Intersegment Eliminations [Member] | Generation ERCOT [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | 1 | 4 | 6
Intersegment Eliminations [Member] | Generation Other Regions [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | (62) | (27) | (62)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | (63) | (48) | (130)
Intersegment Eliminations [Member] | Generation Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | 62 | 53 | 135
Intersegment Eliminations [Member] | Generation All Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties | [1] |  |  |  |  |  |  |  |  | 1 | (5) | (5)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenue from Related Parties |  |  |  |  |  |  |  |  |  | 0 | 0 | 0
Contracts with Customers [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 5,241 | 5,523 | 6,182
Contracts with Customers [Member] | Operating Segments [Member] | Generation Midwest [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 4,527 | 3,923 | 4,007
Contracts with Customers [Member] | Operating Segments [Member] | Generation New England [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 2,660 | 2,064 | 1,953
Contracts with Customers [Member] | Operating Segments [Member] | Generation New York [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 1,723 | 1,605 | 1,198
Contracts with Customers [Member] | Operating Segments [Member] | Generation ERCOT [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 572 | 641 | 810
Contracts with Customers [Member] | Operating Segments [Member] | Generation Other Regions [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 870 | 594 | 670
Contracts with Customers [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 15,593 | 14,350 | 14,820
Contracts with Customers [Member] | Operating Segments [Member] | Generation Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 1,524 | 1,658 | 1,953
Contracts with Customers [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3] |  |  |  |  |  |  |  |  | 17,627 | 16,752 | 17,529
Contracts with Customers [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [1],[3] |  |  |  |  |  |  |  |  | 510 | 744 | 756
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 233 | (8) | 30
Other [Member] | Operating Segments [Member] | Generation Midwest [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 190 | 283 | 395
Other [Member] | Operating Segments [Member] | Generation New England [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 185 | (54) | (175)
Other [Member] | Operating Segments [Member] | Generation New York [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | (36) | (38) | 10
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 560 | 317 | 21
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 686 | 482 | 299
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 1,818 | 982 | 580
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 1,194 | 917 | 193
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [3],[5] |  |  |  |  |  |  |  |  | 2,810 | 1,748 | 228
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | [1],[3],[5] |  |  |  |  |  |  |  |  | $ (202) | $ (151) | $ (545)
[1] | Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $38 million and $52 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 and 2016, respectively, unrealized mark-to-market losses of $262 million, $131 million, and $500 million in 2018, 2017, and 2016, respectively, and elimination of intersegment revenues.
[2] | Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[3] | Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants
[4] | Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory authoritative guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[5] | Includes revenues from derivatives and leases.

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