Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions			3 Months Ended
		Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Mar. 23, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Competitive Energy Revenue			$ 3,392	$ 3,429
Revenue from Purchased Oil and Gas			918	822
Other Operating Income			250	222
Electric Revenue			3,644	2,657
Gas Domestic Regulated Revenue			553	444
Sales Revenue, Services, Other			0	(1)
Net income (loss)			981	123
Assets			117,068			$ 114,904
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			330	268
Net income (loss)			409	257
Assets			48,609			46,974
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			(328)	(266)
Revenue from Purchased Oil and Gas			0	0
Other Operating Income			0	0
Electric Revenue			(8)	(6)
Gas Domestic Regulated Revenue			(3)	(5)
Sales Revenue, Services, Other			(431)	(418)
Operating revenues from affiliates			0	(1)
Net income (loss)			0	(1)
Assets			(11,768)			(11,334)
Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		$ 0	(4)
Gas Domestic Regulated Revenue		0	0
Sales Revenue, Services, Other		0	0
Operating revenues from affiliates		0	(5)
Net income (loss)		12	12
Assets			(4,826)			(4,724)
Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue					$ (4)
Gas Domestic Regulated Revenue					0
Sales Revenue, Services, Other					0
Operating revenues from affiliates					(4)
Net income (loss)					0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			3,720	3,695
Revenue from Purchased Oil and Gas			918	822
Other Operating Income			250	222
Electric Revenue			0	0
Gas Domestic Regulated Revenue			0	0
Sales Revenue, Services, Other			0	0
Net income (loss)			409	257
Assets			48,609			46,974
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			328	266
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			0	0
Revenue from Purchased Oil and Gas			0	0
Other Operating Income			0	0
Electric Revenue			1,298	1,249
Gas Domestic Regulated Revenue			0	0
Sales Revenue, Services, Other			0	0
Net income (loss)			141	115
Assets			28,756			28,335
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			5	5
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			0	0
Revenue from Purchased Oil and Gas			0	0
Other Operating Income			0	0
Electric Revenue			590	644
Gas Domestic Regulated Revenue			206	197
Sales Revenue, Services, Other			0	0
Net income (loss)			127	124
Assets			10,932			10,831
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			1	1
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			0	0
Revenue from Purchased Oil and Gas			0	0
Other Operating Income			0	0
Electric Revenue			667	680
Gas Domestic Regulated Revenue			284	249
Sales Revenue, Services, Other			0	0
Net income (loss)			125	101
Assets			8,821			8,704
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			5	5
Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		90	1,097
Gas Domestic Regulated Revenue		3	66
Sales Revenue, Services, Other		12	12
Operating revenues from affiliates		12	12
Net income (loss)		(309)	140
Assets			21,018			21,025
Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue					1,096
Gas Domestic Regulated Revenue					57
Sales Revenue, Services, Other					0
Operating revenues from affiliates					0
Net income (loss)					19
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			0	0
Revenue from Purchased Oil and Gas			0	0
Other Operating Income			0	0
Electric Revenue			1,097	90
Gas Domestic Regulated Revenue			66	3
Sales Revenue, Services, Other			12	12
Net income (loss)			140	(309)
Assets			21,018			21,025
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			12	12
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue			0	0
Revenue from Purchased Oil and Gas			0	0
Other Operating Income			0	0
Electric Revenue			0	0
Gas Domestic Regulated Revenue			0	0
Sales Revenue, Services, Other			419	405
Net income (loss)			39	(164)
Assets			10,700			10,369
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		3	0
Gas Domestic Regulated Revenue		0	0
Sales Revenue, Services, Other		12	12
Operating revenues from affiliates		12	13
Net income (loss)		22	(15)
Assets			10,785			10,804
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue					42
Gas Domestic Regulated Revenue					1
Sales Revenue, Services, Other					0
Operating revenues from affiliates					0
Net income (loss)					(44)
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			419	405
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			(770)	(695)
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]		(4)	(12)
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			2	6
Potomac Electric Power Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		40	530
Gas Domestic Regulated Revenue		0	0
Sales Revenue, Services, Other		0	0
Operating revenues from affiliates		0	1
Net income (loss)		(140)	58
Assets			7,417			7,335
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue					511
Gas Domestic Regulated Revenue					0
Sales Revenue, Services, Other					0
Operating revenues from affiliates					1
Net income (loss)					32
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		24	296
Gas Domestic Regulated Revenue		3	66
Sales Revenue, Services, Other		0	0
Operating revenues from affiliates		0	2
Net income (loss)		(98)	57
Assets			4,191			4,153
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue					279
Gas Domestic Regulated Revenue					56
Sales Revenue, Services, Other					0
Operating revenues from affiliates					2
Net income (loss)					26
Atlantic City Electric Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		23	275
Gas Domestic Regulated Revenue		0	0
Sales Revenue, Services, Other		0	0
Operating revenues from affiliates		0	1
Net income (loss)		(105)	28
Assets			3,451			$ 3,457
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue					268
Gas Domestic Regulated Revenue					0
Sales Revenue, Services, Other					0
Operating revenues from affiliates					1
Net income (loss)					$ 5
Commonwealth Edison Co Affiliate [Member] | Generation Midwest [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			5	5
PECO Energy Co Affiliate [Member] | Generation Mid Atlantic [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			45	79
Baltimore Gas And Electric Company Affiliate [Member] | Generation Mid Atlantic [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			134	$ 173
PotomacElectricPowerCompanyAffiliate [Member] | Generation Mid Atlantic [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		6	83
DelmarvaPowerandLightCompanyAffiliate [Member] | Generation Mid Atlantic [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		4	51
AtlanticCityElectricCompanyAffiliate [Member] | Generation Mid Atlantic [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ 1	$ 9

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