Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 9,890	$ 8,747
Revenue from Related Parties	0	1
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,165	1,174
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	998	1,002
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	337	314
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	257	190
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	1,430	1,072
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,187	3,752
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	1,326	672
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	46	309
Unrealized Gain (Loss) on Securities	(84)	179
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,559	4,733
Operating Segment [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,160	1,168
Operating Segment [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	998	1,008
Operating Segment [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	337	314
Operating Segment [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	252	183
Operating Segment [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	1,440	1,079
Operating Segment [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,187	3,752
Operating Segment [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	1,326	672
Operating Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Securities	175	132
Operating Segment [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,559	4,733
Corporate, Non-Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	46	309
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(802)	(826)
Revenue from Related Parties	(799)	(824)
Intersegment Eliminations [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	5	6
Intersegment Eliminations [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	(6)
Intersegment Eliminations [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0
Intersegment Eliminations [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	5	7
Intersegment Eliminations [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	(10)	(7)
Intersegment Eliminations [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0
Intersegment Eliminations [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0
Intersegment Eliminations [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0
Intersegment Eliminations [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,174	1,264
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,009	944
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	382	335
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	353	155
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	1,172	1,007
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	4,090	3,705
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	864	503
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,043	4,307
Revenue from Contract with Customer [Member] \| Corporate, Non-Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	89	99
Other [Member] \| Operating Segment [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	(14)	(96)
Other [Member] \| Operating Segment [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	(11)	64
Other [Member] \| Operating Segment [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	(45)	(21)
Other [Member] \| Operating Segment [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	(101)	28
Other [Member] \| Operating Segment [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	268	72
Other [Member] \| Operating Segment [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	97	47
Other [Member] \| Operating Segment [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	462	169
Other [Member] \| Operating Segment [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	516	426
Other [Member] \| Corporate, Non-Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	$ (43)	$ 210

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Amount of unrealized gain (loss) recognized in the income statement on unsold other securities.

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