Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		$ 850	$ 773
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		860	715
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		119	111
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		283	143
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		36	69
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		117	64
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		2,265	1,875
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	[1]	(46)	205
Unrealized Gain (Loss) on Securities		(98)	44
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		2,219	2,080
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	836	755
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	847	704
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	122	115
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	282	143
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	106	94
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	157	108
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	2,350	1,919
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]	(131)	161
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel			(3)
Unrealized Gain (Loss) on Securities		(266)	(49)
Nuclear Fuel Amortization		(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]	2,219	2,080
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		14	18
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		13	11
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(3)	(4)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		1	0
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(70)	(25)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(40)	(44)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(85)	(44)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	[1]	85	44
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 a $3 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended March 31, 2017, unrealized mark-to-market losses of $266 million and $49 million for the three months ended March 31, 2018 and 2017, respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 7 - Early Nuclear Plant Retirements of the Combined Notes to Consolidated Financial Statements of $15 million decrease to revenue net of purchased power and fuel expense for the three months ended March 31, 2018, and the elimination of intersegment revenue net of purchased power and fuel expense.

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