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Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 7,915	$ 7,322	$ 17,805	$ 16,069
Revenue from Related Parties	0	1	0	2
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,091	1,074	2,255	2,247
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	962	962	1,960	1,964
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	381	340	719	655
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	275	234	532	424
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	1,038	804	2,469	1,875
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,747	3,414	7,935	7,165
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	507	353	1,833	1,025
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	(101)	113	(56)	423
Unrealized Gain (Loss) on Securities	(239)	21	(323)	200
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,153	3,880	9,712	8,613
Operating Segment [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,086	1,065	2,244	2,232
Operating Segment [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	962	962	1,959	1,970
Operating Segment [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	381	341	719	656
Operating Segment [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	271	227	523	411
Operating Segment [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	1,047	819	2,490	1,896
Operating Segment [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,747	3,414	7,935	7,165
Operating Segment [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	507	353	1,833	1,025
Operating Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Securities	314	85	489	218
Operating Segment [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	4,153	3,880	9,712	8,613
Corporate, Non-Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	(101)	113	(56)	423
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(794)	(760)	(1,594)	(1,587)
Revenue from Related Parties	(794)	(760)	(1,594)	(1,585)
Intersegment Eliminations [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	5	9	11	15
Intersegment Eliminations [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0	1	(6)
Intersegment Eliminations [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	(1)	0	(1)
Intersegment Eliminations [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	4	7	9	13
Intersegment Eliminations [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	(9)	(15)	(21)	(21)
Intersegment Eliminations [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0	0	0
Intersegment Eliminations [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0	0	0
Intersegment Eliminations [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0	0	0
Intersegment Eliminations [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	0	0	0	0
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	1,062	1,100	2,233	2,365
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	975	855	1,983	1,798
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	376	336	759	672
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	179	175	533	330
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	921	776	2,095	1,782
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	3,513	3,242	7,603	6,947
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	253	209	1,117	712
Revenue from Contract with Customer [Member] \| Operating Segment [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	3,873	3,537	8,915	7,844
Revenue from Contract with Customer [Member] \| Corporate, Non-Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	107	86	195	185
Other [Member] \| Operating Segment [Member] \| Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	24	(35)	11	(133)
Other [Member] \| Operating Segment [Member] \| Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	(13)	107	(24)	172
Other [Member] \| Operating Segment [Member] \| Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	5	5	(40)	(16)
Other [Member] \| Operating Segment [Member] \| Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	92	52	(10)	81
Other [Member] \| Operating Segment [Member] \| Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	126	43	395	114
Other [Member] \| Operating Segment [Member] \| Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	234	172	332	218
Other [Member] \| Operating Segment [Member] \| Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	254	144	716	313
Other [Member] \| Operating Segment [Member] \| Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	280	343	797	769
Other [Member] \| Corporate, Non-Segment [Member] \| Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	$ (208)	$ 27	$ (251)	$ 238