Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	$ 652	$ 735	$ 1,334	$ 1,586
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	730	772	1,500	1,631
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	253	266	519	549
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	79	82	154	118
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	134	186	292	424
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	1,848	2,041	3,799	4,308
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	70	258	210	209
Unrealized Gain (Loss) on Securities	38	5	(102)	175
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	1,918	2,299	4,009	4,517
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	644	722	1,324	1,558
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	738	770	1,506	1,617
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	250	259	512	541
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	80	129	178	235
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	154	229	328	511
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	1,866	2,109	3,848	4,462
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	52	190	161	55
Unrealized Gain (Loss) on Securities	(74)	90	(14)	102
Nuclear Fuel Amortization	5	20	9	34
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	1,918	2,299	4,009	4,517
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	8	13	10	28
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(8)	2	(6)	14
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	3	7	7	8
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(1)	(47)	(24)	(117)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(20)	(43)	(36)	(87)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(18)	(68)	(49)	(154)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	18	68	49	154
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