Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	$ 572	$ 525	$ 1,141	$ 1,092
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	658	703	1,360	1,427
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	292	246	536	440
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	83	97	(1,102)	177
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	136	157	353	312
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	1,741	1,728	2,288	3,448
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	465	210	867	519
Unrealized Gain (Loss) on Securities	(239)	21	(323)	200
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	2,206	1,938	3,155	3,967
Operating Segment [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	567	516	1,130	1,074
Operating Segment [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	658	702	1,359	1,431
Operating Segment [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	289	243	531	433
Operating Segment [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	80	92	(957)	168
Operating Segment [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	157	181	409	355
Operating Segment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	1,751	1,734	2,472	3,461
Operating Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	455	204	683	506
Unrealized Gain (Loss) on Securities	314	85	489	218
Accelerated nuclear fuel amortization			106
Operating Segment [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,206	1,938	3,155	3,967
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	5	9	11	18
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	0	1	1	(4)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	3	3	5	7
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	3	5	(145)	9
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(21)	(24)	(56)	(43)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(10)	(6)	(184)	(13)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	10	6	184	13
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	$ 0	$ 0	$ 0	$ 0