Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended						6 Months Ended	9 Months Ended
	Sep. 30, 2016		Jun. 30, 2016	Mar. 23, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2016		Sep. 30, 2015		Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 9,002				$ 7,401			$ 23,486		$ 22,746
Competitive Energy Revenue	3,823				4,095			10,559		11,796
Electric Revenue	4,330				2,721			10,461		7,564
Other Operating Income	386				122			169		581
Revenue from Purchased Oil and Gas	326				347			1,515		1,901
Operating revenues from affiliates	1				2
Net income (loss)	526				587			956		1,959
Assets	114,535						$ 114,535	114,535				$ 95,384
Gas Domestic Regulated Revenue	137				116			781		904
Sales Revenue, Services, Other	0				0			1		0
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue					0			0		0
Electric Revenue	0				0			0		0
Other Operating Income					0			0		0
Revenue from Purchased Oil and Gas					0			0		0
Net income (loss)	(125)				(36)			(340)		(96)
Assets	9,883						9,883	9,883				15,389
Gas Domestic Regulated Revenue	0				0			0		0
Sales Revenue, Services, Other	362				348			1,166		1,007
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	(499)				(204)			(1,118)		(564)
Electric Revenue	(8)				(1)			(24)		(3)
Other Operating Income	(1)				0			(2)		1
Revenue from Purchased Oil and Gas	0				0			0		0
Operating revenues from affiliates	(885)				(555)			3		3
Net income (loss)	(1)				(2)			(3)		(3)
Assets	(11,897)						(11,897)	(11,897)				(11,728)
Gas Domestic Regulated Revenue	(5)				(3)			(10)		(12)
Sales Revenue, Services, Other	(373)				(348)			(1,199)		(1,007)
Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	(4)						(9)
Operating revenues from affiliates	(4)						(9)
Net income (loss)	11						34
Assets	(4,743)						(4,743)	(4,743)
Gas Domestic Regulated Revenue							0
Sales Revenue, Services, Other	0						0
Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue				$ (4)	0					0
Operating revenues from affiliates				(4)	(3)					(10)
Net income (loss)				0	0					0
Assets												(5,238)
Gas Domestic Regulated Revenue				0	0					0
Sales Revenue, Services, Other				0	0					0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	4,322				4,299			11,677		12,360
Electric Revenue	0				0			0		0
Other Operating Income	387				122			171		580
Revenue from Purchased Oil and Gas	326				347			1,515		1,901
Net income (loss)	271				332			556		1,208
Assets	47,568						47,568	47,568				46,529
Gas Domestic Regulated Revenue	0				0			0		0
Sales Revenue, Services, Other	0				0			0		0
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	500				205			1,121		567
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	1,164				1,151			3,343		3,633
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,163	[1]			1,152	[1]		3,330	[2]	3,634	[2]
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	1				(1)			13		(1)
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	0				0			0		0
Electric Revenue	1,497				1,376			4,031		3,709
Other Operating Income	0				0			0		0
Revenue from Purchased Oil and Gas	0				0			0		0
Net income (loss)	37				149			297		339
Assets	28,020						28,020	28,020				26,532
Gas Domestic Regulated Revenue	0				0			0		0
Sales Revenue, Services, Other	0				0			0		0
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	4				1			12		3
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	0				0			0		0
Electric Revenue	740				691			1,971		1,950
Other Operating Income	0				0			0		0
Revenue from Purchased Oil and Gas	0				0			0		0
Net income (loss)	122				90			346		299
Assets	11,041						11,041	11,041				10,367
Gas Domestic Regulated Revenue	48				49			322		436
Sales Revenue, Services, Other	0				0			0		0
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	2				1			5		1
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	0				0			0		0
Electric Revenue	735				655			1,998		1,908
Other Operating Income	0				0			0		0
Revenue from Purchased Oil and Gas	0				0			0		0
Net income (loss)	56				54			191		212
Assets	8,857						8,857	8,857				8,295
Gas Domestic Regulated Revenue	77				70			423		480
Sales Revenue, Services, Other	0				0			0		0
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	7				3			16		10
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates								1,166		1,003
Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	1,366						2,485
Net income (loss)	166						(91)
Gas Domestic Regulated Revenue	17						46
Sales Revenue, Services, Other	11						34
Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue				1,096	1,317					3,680
Net income (loss)				19
Gas Domestic Regulated Revenue				57	19					129
Sales Revenue, Services, Other				0	0					0
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	0						3
Operating revenues from affiliates	11						35
Net income (loss)	(15)						(16)
Assets	11,057						11,057	11,057
Gas Domestic Regulated Revenue	0						0
Sales Revenue, Services, Other	11						34
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue				42	44					161
Operating revenues from affiliates				0	0					0
Net income (loss)				(44)	(6)					(23)
Assets												7,162
Gas Domestic Regulated Revenue				1	0					0
Sales Revenue, Services, Other				0	0					0
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue	0							0		0
Electric Revenue	1,366				0			2,485		0
Other Operating Income	0							0		0
Revenue from Purchased Oil and Gas	0							0		0
Operating revenues from affiliates	11						34
Net income (loss)	166				0			(91)		0
Assets	21,063						21,063	21,063				0
Gas Domestic Regulated Revenue	17				0			46		0
Sales Revenue, Services, Other	11				0			34		0
Pepco Holdings LLC [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates				0	0					0
Net income (loss)					91					197
Assets												16,188
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	11				0			34		0
Corporate, Non-Segment [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	362				347
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates								(2,351)		(1,581)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	5,035				4,768			13,363		14,841
Generation Total Consolidated Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	5,035	[1]			4,768	[1]		13,363	[2]	14,841	[2]
Generation Total Consolidated Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0				0			0		0
Potomac Electric Power Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	635		$ 1,184
Operating revenues from affiliates	1						2
Net income (loss)	79						(12)
Assets	7,219						7,219	7,219
Gas Domestic Regulated Revenue	0		0
Sales Revenue, Services, Other	0		0
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue				511	592					1,641
Operating revenues from affiliates				1	1					4
Net income (loss)				32	60					128
Assets												6,908
Gas Domestic Regulated Revenue				0	0					0
Sales Revenue, Services, Other				0	0					0
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	314		593
Operating revenues from affiliates	2						4
Net income (loss)	44						(42)
Assets	4,023						4,023	4,023
Gas Domestic Regulated Revenue	17		46
Sales Revenue, Services, Other	0		0
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue				279	295					875
Operating revenues from affiliates				2	1					4
Net income (loss)				26	15					55
Assets												3,969
Gas Domestic Regulated Revenue				56	19					129
Sales Revenue, Services, Other				0	0					0
Atlantic City Electric Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	421		714
Operating revenues from affiliates	1						2
Net income (loss)	47						(55)
Assets	3,507						$ 3,507	3,507
Gas Domestic Regulated Revenue	0		0
Sales Revenue, Services, Other	0		$ 0
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue				268	386					1,003
Operating revenues from affiliates				1	1					2
Net income (loss)				5	22					37
Assets												$ 3,387
Gas Domestic Regulated Revenue				0	0					0
Sales Revenue, Services, Other				$ 0	0					0
PECO Energy Co Affiliate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues								234		173
PECO Energy Co Affiliate [Member] | Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	91				61
Baltimore Gas And Electric Company Affiliate [Member] | Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	183				141			489		376
Commonwealth Edison Co Affiliate [Member] | Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	20				$ 2			$ 38		$ 17
PotomacElectricPowerCompanyAffiliate [Member] | Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	128
PotomacElectricPowerCompanyAffiliate [Member] | Generation Midwest [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	223
DelmarvaPowerandLightCompanyAffiliate [Member] | Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	63
DelmarvaPowerandLightCompanyAffiliate [Member] | Generation Midwest [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	109
AtlanticCityElectricCompanyAffiliate [Member] | Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	15
AtlanticCityElectricCompanyAffiliate [Member] | Generation Midwest [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	$ 28

[1] Three Months Ended September 30, 2016 Three Months Ended September 30, 2015 Revenuesfrom externalcustomers(a)IntersegmentrevenuesTotalRevenuesRevenuesfrom externalcustomers(a)(c)Intersegmentrevenues(c)TotalRevenues(c)Mid-Atlantic$1,813 $(13) $1,800 $1,640 $(8) $1,632Midwest1,163 1 1,164 1,152 (1) 1,151New England455 (4) 451 520 — 520New York331 (8) 323 254 (4) 250ERCOT289 6 295 317 (1) 316Other Power Regions271 (33) 238 416 (40) 376Total Revenues for Reportable Segments4,322 (51) 4,271 4,299 (54) 4,245Other(b)713 51 764 469 54 523Total Generation Consolidated Operating Revenues$5,035 $— $5,035 $4,768 $— $4,768

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