Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	$ 591	$ 689	$ 1,683	$ 2,023
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	750	747	2,178	2,247
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	285	291	725	810
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	147	72	325	225
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	225	184	538	478
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	1,998	1,983	5,449	5,783
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	347	140	862	349
Unrealized Gain (Loss) on Securities	37	77	238	64
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	2,345	2,123	6,311	6,132
Operating Segment [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	586	684	1,660	2,007
Operating Segment [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	748	763	2,180	2,269
Operating Segment [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	281	288	714	800
Operating Segment [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	141	76	311	252
Operating Segment [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	253	212	608	542
Operating Segment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,009	2,023	5,473	5,870
Operating Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	336	100	838	262
Revenue Net of Purchase Power And Fuel		(3)		(13)
Unrealized Gain (Loss) on Securities	255	17	472	(84)
Accelerated nuclear fuel amortization	24		24
Asset Impairment Charges	10		10
Operating Segment [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	2,345	2,123	6,311	6,132
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	5	5	23	16
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	2	(16)	(2)	(22)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	4	3	11	10
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	6	(4)	14	(27)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(28)	(28)	(70)	(64)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(11)	(40)	(24)	(87)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	11	40	24	87
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