Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total				$ 19
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		$ 3,317	$ 3,571	3,431
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		2,971	2,892	2,599
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		438	461	351
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		742	634	483
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		281	293	317
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	[1]	336	250	327
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		8,085	8,101	7,508
Generation Reportable Segments Total [Member] | Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers				11
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity				8
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total	[2]	836	1,013	(40)
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel		(57)	8	(124)
Derivative, Gain on Derivative			(257)
Derivative, Loss on Derivative		41		591
Generation All Other Segments [Member] | Scenario, Adjustment [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers				(11)
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity				(8)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense, Total		8,921	9,114	7,468
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	3,282	3,556	3,544
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	2,969	2,912	2,607
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	467	519	450
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	761	584	439
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	412	425	573
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[1],[3]	483	440	517
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	8,374	8,436	8,130
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[2],[3]	547	678	(662)
Derivative, Gain on Derivative			(203)
Derivative, Loss on Derivative		500		174
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from external customers	[3]	8,921	9,114	7,468
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		35	15	(113)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		2	(20)	(8)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(29)	(58)	(99)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(19)	50	44
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(131)	(132)	(256)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	[1]	(147)	(190)	(190)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		(289)	(335)	(622)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity	[2]	289	335	622
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue net of purchased power and fuel expense from transactions with other operating segments of the same entity		$ 0	$ 0	$ 0

[1] (b)Includes purchases and sales from third parties and affiliated sales to the Utility Registrants.

[2] (c)Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $57 million decrease in RNF, a $8 million increase in RNF, and a $124 million decrease in RNF for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2016, 2015, and 2014, respectively, unrealized mark-to-market losses of $41 million, gains of $257 million, and losses of $591 million for the years ended December 31, 2016, 2015, and 2014, respectively, accelerated nuclear fuel amortization associated with the initial early retirement decision for Clinton and Quad Cities as discussed in Note 9 - Early Nuclear Plant Retirements of $60 million for the year ended December 31, 2016, and the elimination of intersegment revenues net of purchased power and fuel expense.

[3] (a)On April 1, 2014, Generation assumed operational control of CENG's nuclear fleet. As a result, beginning on April 1, 2014, CENG's revenues net of purchased power and fuel expense are included on a fully consolidated basis.