Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		$ 683	$ 850
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		771	860
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		265	283
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		74	36
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		156	236
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		1,949	2,265
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	[1]	142	(46)
Unrealized Gain (Loss) on Securities		(52)	(98)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		2,091	2,219
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	679	836
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	769	847
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	262	282
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	98	106
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	174	279
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	1,982	2,350
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[1],[2]	109	(131)
Unrealized Gain (Loss) on Securities		(28)	(266)
Nuclear Fuel Amortization		5	15
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	2,091	2,219
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		4	14
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		2	13
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		3	1
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(24)	(70)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(18)	(43)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(33)	(85)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	[1]	33	85
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		$ 0	$ 0

[1] Other represents activities not allocated to a region. See text above for a description of included activities. Includes unrealized mark-to-market losses of $28 million and $266 million in 2019 and 2018, respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 — Early Plant Retirements of $5 million and $15 million decrease to RNF in 2019 and 2018, respectively, and the elimination of intersegment RNF.

[2] Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants.