Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended							6 Months Ended
		Jun. 30, 2017		Jun. 30, 2016		Jun. 30, 2016		Mar. 23, 2016	Jun. 30, 2017		Jun. 30, 2016		Dec. 31, 2016
Segment Reporting Information [Line Items]
Competitive Energy Revenue		$ 3,453	[1]	$ 3,301	[1]				$ 6,845	[2]	$ 6,732	[2]
Revenue from Purchased Oil and Gas		430	[1]	367	[1]				1,348	[2]	1,189	[2]
Other Operating Income		25	[1]	(434)	[1]				275	[2]	(213)	[2]
Electric Revenue		3,511	[1]	3,480	[1]				7,156	[2]	6,136	[2]
Gas Domestic Regulated Revenue		204	[1]	197	[1]				757	[2]	641	[2]
Sales Revenue, Services, Other		0	[1]	(1)	[1]				0	[2]	0	[2]
Operating revenues from affiliates		0	[3]	1	[3]				0	[4]	2	[4]
Net income (loss)		64		306					1,046		430
Assets		117,104							117,104				$ 114,904
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		268		358					598		627
Net income (loss)		(266)		28					144		285
Assets		48,130							48,130				46,974
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue		(266)	[1]	(354)	[1]				(592)	[2]	(620)	[2]
Revenue from Purchased Oil and Gas		0	[1]	0	[1]				0	[2]	0	[2]
Other Operating Income		0	[1]	(1)	[1]				(1)	[2]	(1)	[2]
Electric Revenue		(7)	[1]	(7)	[1]				(16)	[2]	(15)	[2]
Gas Domestic Regulated Revenue		(1)	[1]	(2)	[1]				(4)	[2]	(5)	[2]
Sales Revenue, Services, Other		(461)	[1]	(409)	[1]				(893)	[2]	(826)	[2]
Operating revenues from affiliates		(734)	[3]	(771)	[3]				(1,503)	[4]	(1,466)	[4]
Net income (loss)		0		(1)					0		(2)
Assets		(11,986)							(11,986)				(11,334)
Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		(4)	[5]	(4)	[5]	$ (5)	[6]		(9)	[6]
Gas Domestic Regulated Revenue		0	[5]	0	[5]	0	[6]		0	[6]
Sales Revenue, Services, Other		(1)	[5]	0	[5]	0	[6]		(2)	[6]
Operating revenues from affiliates		(5)		(4)		(5)			(9)
Net income (loss)		12		10		23			23
Assets		(4,971)							(4,971)				(4,724)
Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	[6]							$ (4)
Gas Domestic Regulated Revenue	[6]							0
Sales Revenue, Services, Other	[6]							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		3,719	[1],[7]	3,655	[1],[7]				7,437	[2],[8]	7,352	[2],[8]
Revenue from Purchased Oil and Gas		430	[1],[7]	367	[1],[7]				1,348	[2],[8]	1,189	[2],[8]
Other Operating Income		25	[1],[7]	(433)	[1],[7]				276	[2],[8]	(212)	[2],[8]
Electric Revenue		0	[1],[7]	0	[1],[7]				0	[2],[8]	0	[2],[8]
Gas Domestic Regulated Revenue		0	[1],[7]	0	[1],[7]				0	[2],[8]	0	[2],[8]
Sales Revenue, Services, Other		0	[1],[7]	0	[1],[7]				0	[2],[8]	0	[2],[8]
Net income (loss)		(266)	[7]	28	[7]				144	[8]	285	[8]
Assets	[7]	48,130							48,130				46,974
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		266	[3],[7]	355	[3],[7]				594	[4],[8]	621	[4],[8]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue		0	[1]	0	[1]				0	[2]	0	[2]
Revenue from Purchased Oil and Gas		0	[1]	0	[1]				0	[2]	0	[2]
Other Operating Income		0	[1]	0	[1]				0	[2]	0	[2]
Electric Revenue		1,357	[1]	1,286	[1]				2,656	[2]	2,535	[2]
Gas Domestic Regulated Revenue		0	[1]	0	[1]				0	[2]	0	[2]
Sales Revenue, Services, Other		0	[1]	0	[1]				0	[2]	0	[2]
Net income (loss)		118		145					259		260
Assets		29,160							29,160				28,335
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[3]	3	[3]				9	[4]	8	[4]
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue		0	[1]	0	[1]				0	[2]	0	[2]
Revenue from Purchased Oil and Gas		0	[1]	0	[1]				0	[2]	0	[2]
Other Operating Income		0	[1]	0	[1]				0	[2]	0	[2]
Electric Revenue		550	[1]	587	[1]				1,140	[2]	1,232	[2]
Gas Domestic Regulated Revenue		80	[1]	77	[1]				286	[2]	273	[2]
Sales Revenue, Services, Other		0	[1]	0	[1]				0	[2]	0	[2]
Net income (loss)		88		100					215		224
Assets		11,041							11,041				10,831
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	[3]	2	[3]				3	[4]	4	[4]
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue		0	[1]	0	[1]				0	[2]	0	[2]
Revenue from Purchased Oil and Gas		0	[1]	0	[1]				0	[2]	0	[2]
Other Operating Income		0	[1]	0	[1]				0	[2]	0	[2]
Electric Revenue		571	[1]	584	[1]				1,237	[2]	1,264	[2]
Gas Domestic Regulated Revenue		103	[1]	96	[1]				388	[2]	345	[2]
Sales Revenue, Services, Other		0	[1]	0	[1]				0	[2]	0	[2]
Net income (loss)		45		34					169		135
Assets		8,786							8,786				8,704
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[3]	4	[3]				8	[4]	9	[4]
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue		0	[1],[9]	0	[1],[9]				0	[2],[10]	0	[2],[10]
Revenue from Purchased Oil and Gas		0	[1],[9]	0	[1],[9]				0	[2],[10]	0	[2],[10]
Other Operating Income		0	[1],[9]	0	[1],[9]				0	[2],[10]	0	[2],[10]
Electric Revenue		1,040	[1],[5],[9]	1,030	[1],[5],[9]	1,120	[6]		2,138	[2],[6],[10]	1,120	[2],[10]
Gas Domestic Regulated Revenue		22	[1],[5],[9]	26	[1],[5],[9]	28	[6]		87	[2],[6],[10]	28	[2],[10]
Sales Revenue, Services, Other		12	[1],[5],[9]	10	[1],[5],[9]	23	[6]		23	[2],[6],[10]	23	[2],[10]
Net income (loss)		66	[9]	52	[9]	(257)			205	[10]	(257)	[10]
Assets	[9]	21,190							21,190				21,025
Pepco Holdings LLC [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	[6]							1,096
Gas Domestic Regulated Revenue	[6]							57
Sales Revenue, Services, Other	[6]							0
Net income (loss)								19
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		12	[3],[9]	10	[3],[9]	23			23	[4],[10]	23	[4],[10]
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates								0
Potomac Electric Power Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		514	[5]	509	[5]	550	[6]		1,045	[6]
Gas Domestic Regulated Revenue		0	[5]	0	[5]	0	[6]		0	[6]
Sales Revenue, Services, Other		0	[5]	0	[5]	0	[6]		0	[6]
Net income (loss)		43		49		(92)			101
Assets		7,648							7,648				7,335
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	[6]							511
Gas Domestic Regulated Revenue	[6]							0
Sales Revenue, Services, Other	[6]							0
Net income (loss)								32
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		1		2			3
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates								1
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		260	[5]	255	[5]	279	[6]		557	[6]
Gas Domestic Regulated Revenue		22	[5]	26	[5]	29	[6]		87	[6]
Sales Revenue, Services, Other		0	[5]	0	[5]	0	[6]		0	[6]
Net income (loss)		19		12		(86)			76
Assets		4,235							4,235				4,153
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	[6]							279
Gas Domestic Regulated Revenue	[6]							56
Sales Revenue, Services, Other	[6]							0
Net income (loss)								26
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2		2			4
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates								2
Atlantic City Electric Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		270	[5]	270	[5]	293	[6]		544	[6]
Gas Domestic Regulated Revenue		0	[5]	0	[5]	0	[6]		0	[6]
Sales Revenue, Services, Other		0	[5]	0	[5]	0	[6]		0	[6]
Net income (loss)		8		3		(102)			36
Assets		3,478							3,478				3,457
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	[6]							268
Gas Domestic Regulated Revenue	[6]							0
Sales Revenue, Services, Other	[6]							0
Net income (loss)								5
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		1		1			1
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates								1
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive Energy Revenue		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Revenue from Purchased Oil and Gas		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Other Operating Income		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Electric Revenue		0	[1],[11]	0	[1],[11]				1	[2],[12]	0	[2],[12]
Gas Domestic Regulated Revenue		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Sales Revenue, Services, Other		449	[1],[11]	398	[1],[11]				870	[2],[12]	803	[2],[12]
Net income (loss)		13	[11]	(52)	[11]				54	[12]	(215)	[12]
Assets	[11]	10,783							10,783				10,369
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Electric Revenue		0	[5],[13]	0	[5],[13]	3	[6],[14]		1	[6],[14]
Gas Domestic Regulated Revenue		0	[5],[13]	0	[5],[13]	(1)	[6],[14]		0	[6],[14]
Sales Revenue, Services, Other		13	[5],[13]	10	[5],[13]	23	[6],[14]		25	[6],[14]
Net income (loss)		(16)	[13]	(22)	[13]	0	[14]		(31)	[14]
Assets	[13]	10,800							10,800				$ 10,804
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Electric Revenue	[6],[14]							42
Gas Domestic Regulated Revenue	[6],[14]							1
Sales Revenue, Services, Other	[6],[14]							0
Net income (loss)	[14]							(44)
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		448	[3],[11]	398	[3],[11]				866	[4],[12]	803	[4],[12]
Corporate and Other [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		13	[13]	10	[13]	23	[14]		24	[14]
Corporate and Other [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[14]							$ 0
Generation Mid Atlantic [Member] | PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		34		64					79		143
Generation Mid Atlantic [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		99		135					233		306
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		68		88		94			152
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		40		43		47			91
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7		12		$ 13			16
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		9		(16)					5		(28)
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		18		13					23		18
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (8)		$ 7					$ (5)		$ 13

[1] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended June 30, 2017 and 2016.

[2] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the six months ended June 30, 2017 and 2016.

[3] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

[4] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

[5] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended June 30, 2017 and 2016.

[6] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the six months ended June 30, 2017 and 2016.

[7] Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. Intersegment revenues for Generation for the three months ended June 30, 2017 include revenue from sales to PECO of $34 million, sales to BGE of $99 million, sales to Pepco of $68 million, sales to DPL of $40 million, and sales to ACE of $7 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region. For the three months ended June 30, 2016, intersegment revenues for Generation include revenue from sales to PECO of $64 million, sales to BGE of $135 million, sales to Pepco of $88 million, sales to DPL of $43 million, and sales to ACE of $12 million in the Mid-Atlantic region, and sales to ComEd of $13 million in the Midwest region.

[8] Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. Intersegment revenues for Generation for the six months ended June 30, 2017 include revenue from sales to PECO of $79 million, sales to BGE of $233 million, sales to Pepco of $152 million, sales to DPL of $91 million, and sales to ACE of $16 million in the Mid-Atlantic region, and sales to ComEd of $23 million in the Midwest region. For the six months ended June 30, 2016, intersegment revenues for Generation include revenue from sales to PECO of $143 million and sales to BGE of $306 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region. For the Successor period of March 24, 2016 to June 30, 2016, intersegment revenues for Generation include revenue from sales to Pepco of $94 million, sales to DPL of $47 million, and sales to ACE of $13 million in the Mid-Atlantic region.

[9] Amounts included represent activity for PHI's successor period, three months ended June 30, 2017 and 2016. PHI includes the three reportable segments: Pepco, DPL and ACE.

[10] Amounts included represent activity for PHI's successor period, six months ended June 30, 2017 and March 24, 2016 through June 30, 2016. PHI includes the three reportable segments: Pepco, DPL and ACE. See tables below for PHI's predecessor period, including Pepco, DPL and ACE, for January 1, 2016 to March 23, 2016.

[11] Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.

[12] Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.

[13] Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities.

[14] Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. For the predecessor period presented, Other includes the activity of PHI’s unregulated businesses which were distributed to Exelon and Generation as a result of the PHI Merger.