Segment Information Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		$ 3,073	$ 3,214	$ 3,317
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		3,135	2,820	2,971
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		354	514	438
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		1,122	1,008	752
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		258	332	281
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		375	305	336
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		8,317	8,193	8,095
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	[1]	427	617	832
Unrealized Gain (Loss) on Securities		(262)	(131)	(500)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		8,744	8,810	8,927
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	3,022	3,105	3,282
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	3,112	2,810	2,969
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	368	538	467
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	1,112	1,007	771
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	501	575	412
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	515	476	483
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	8,630	8,511	8,384
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[1],[2]	114	299	543
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel			54	57
Unrealized Gain (Loss) on Securities		(319)	(175)	(41)
Nuclear Fuel Amortization		(57)	(12)	(60)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	8,744	8,810	8,927
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		51	109	35
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		23	10	2
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(14)	(24)	(29)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		10	1	(19)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(243)	(243)	(131)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(140)	(171)	(147)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(313)	(318)	(289)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	[1]	313	318	289
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		$ 0	$ 0	$ 0

[1] Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million and $57 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 and 2016, respectively, unrealized mark-to-market losses of $319 million, $175 million, and $41 million in 2018, 2017, and 2016, respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $57 million, $12 million and $60 million for the year ended December 31, 2018, 2017, and 2016 and the elimination of intersegment RNF.

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