Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	$ 567	$ 567
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	702	727
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	242	193
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	(1,184)	80
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	217	158
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	544	1,725
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	405	304
Unrealized Gain (Loss) on Securities	(84)	179
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	949	2,029
Operating Segment [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	562	559
Operating Segment [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	702	732
Operating Segment [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	240	189
Operating Segment [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	(1,036)	76
Operating Segment [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	250	177
Operating Segment [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	718	1,733
Operating Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	231	296
Unrealized Gain (Loss) on Securities	175	132
Accelerated nuclear fuel amortization	54
Operating Segment [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	949	2,029
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	5	8
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	0	(5)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	2	4
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(148)	4
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(33)	(19)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(174)	(8)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	174	8
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	$ 0	$ 0