Segment Information Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Nuclear Fuel Amortization	[1]	$ 1,096	$ 1,159	$ 1,116
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Total RNF		3,214	3,317	3,571
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Total RNF		2,820	2,971	2,892
Generation New England [Member]
Segment Reporting Information [Line Items]
Total RNF		514	438	461
Generation New York [Member]
Segment Reporting Information [Line Items]
Total RNF		976	742	634
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Total RNF		332	281	293
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Total RNF		305	336	250
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Total RNF		8,161	8,085	8,101
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Total RNF	[2]	615	836	1,013
Unrealized Gain (Loss) on Securities		(131)	(500)	203
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Total RNF		8,776	8,921	9,114
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	3,105	3,282	3,556
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	2,810	2,969	2,912
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	538	467	519
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	975	761	584
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	575	412	425
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	476	483	440
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	8,479	8,374	8,436
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2],[3]	297	547	678
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel		(54)	(57)	8
Unrealized Gain (Loss) on Securities		(175)	(41)	257
Nuclear Fuel Amortization		12	60
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	8,776	8,921	9,114
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		109	35	15
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		10	2	(20)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(24)	(29)	(58)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		1	(19)	50
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(243)	(131)	(132)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(171)	(147)	(190)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(318)	(289)	(335)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	[2]	318	289	335
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		$ 0	$ 0	$ 0

[1] Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[2] Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million decrease in RNF, a $57 million decrease in RNF, and a $8 million increase in RNF for the amortization of intangible assets and liabilities related to commodity contracts for the years ended December 31, 2017, 2016, and 2015, respectively, unrealized mark-to-market losses of $175 million, losses of $41 million, and gains of $257 million for the years ended December 31, 2017, 2016, and 2015, respectively, accelerated nuclear fuel amortization associated with the announced early retirement decision for Clinton and Quad Cities as discussed in Note 8 - Early Nuclear Plant Retirements of $12 million and $60 million for the year ended December 31, 2017 and 2016, and the elimination of intersegment revenues net of purchased power and fuel expense.

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