Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Rate-regulated electric revenues				$ 0				$ 0
Rate-regulated natural gas revenues				0				0
Revenues		$ 9,403		8,768		$ 27,170		25,180
Operating revenues from affiliates		0	[1]	0	[1]	0	[2]	0
Net income (loss)		800		865		1,979		1,928
Assets	[3]	119,485				119,485				$ 116,770
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		1,340		1,278		3,541		3,376
Rate-regulated natural gas revenues		23		18		129		105
Revenues		1,361		1,310		3,688		3,557
Operating revenues from affiliates		3		12		11		35
Net income (loss)		187		153		336		359
Assets	[4]	21,957				21,957				21,247
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues				0				0
Rate-regulated natural gas revenues				0				0
Revenues		5,278		4,750		15,368		13,843
Operating revenues from affiliates		308		296		979		894
Net income (loss)		300		346		667		508
Assets	[5]	48,207				48,207				48,457
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		4,435	[6]	3,746	[6]	12,221	[7]	10,626	[7]
Competitive businesses natural gas revenues		397	[6]	460	[6]	1,831	[7]	1,807	[7]
Competitive businesses other revenues		139	[6]	249	[6]	335	[7]	522	[7]
Rate-regulated electric revenues		4,270	[6]	4,164	[6]	11,766	[7]	11,318	[7]
Rate-regulated natural gas revenues		162	[6]	149	[6]	1,017	[7]	906	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	1	[7]
Revenues		9,403	[6]	8,768	[6]	27,170	[7]	25,180	[7]
Net income (loss)		800		865		1,979		1,928
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		(306)	[6]	(295)	[6]	(969)	[7]	(888)	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	(8)	[7]	0	[7]
Competitive businesses other revenues		(1)	[6]	0	[6]	(4)	[7]	0	[7]
Rate-regulated electric revenues		(7)	[6]	(7)	[6]	(34)	[7]	(23)	[7]
Rate-regulated natural gas revenues		(5)	[6]	(2)	[6]	(13)	[7]	(6)	[7]
Shared service and other revenues		(461)	[6]	(458)	[6]	(1,408)	[7]	(1,350)	[7]
Revenues		(780)	[6]	(762)	[6]	(2,436)	[7]	(2,267)	[7]
Operating revenues from affiliates		(779)	[1]	(759)	[1]	(2,430)	[2]	(2,262)	[2]
Net income (loss)		0		0		0		(2)
Assets		(10,378)				(10,378)				(10,552)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		(4)	[8]	(3)	[8]	(12)	[9]	(13)	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		(100)	[8]	0	[8]	(316)	[9]	(2)	[9]
Revenues		(104)	[8]	(3)	[8]	(328)	[9]	(15)	[9]
Operating revenues from affiliates		(105)		(4)		(327)		(14)
Net income (loss)		3		12		11		35
Assets		(5,300)				(5,300)				(4,987)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		4,741	[6],[10]	4,041	[6],[10]	13,190	[7],[11]	11,514	[7],[11]
Competitive businesses natural gas revenues		397	[6],[10]	460	[6],[10]	1,839	[7],[11]	1,807	[7],[11]
Competitive businesses other revenues		140	[6],[10]	249	[6],[10]	339	[7],[11]	522	[7],[11]
Rate-regulated electric revenues		0	[6],[10]	0	[6],[10]	0	[7],[11]	0	[7],[11]
Rate-regulated natural gas revenues		0	[6],[10]	0	[6],[10]	0	[7],[11]	0	[7],[11]
Shared service and other revenues		0	[6],[10]	0	[6],[10]	0	[7],[11]	0	[7],[11]
Revenues		5,278	[6],[10]	4,750	[6],[10]	15,368	[7],[11]	13,843	[7],[11]
Net income (loss)		300	[10]	346	[10]	667	[11]	508	[11]
Assets	[10]	48,207				48,207				48,457
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		308	[1],[10]	294	[1],[10]	981	[2],[11]	888	[2],[11]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		1,598	[6]	1,571	[6]	4,508	[7]	4,227	[7]
Rate-regulated natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		1,598	[6]	1,571	[6]	4,508	[7]	4,227	[7]
Net income (loss)		193		189		523		447
Assets		31,119				31,119				29,726
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		4	[1]	3	[1]	23	[2]	12	[2]
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		700	[6]	662	[6]	1,893	[7]	1,802	[7]
Rate-regulated natural gas revenues		57	[6]	53	[6]	382	[7]	339	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		757	[6]	715	[6]	2,275	[7]	2,141	[7]
Net income (loss)		126		112		336		327
Assets		10,621				10,621				10,170
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	[1]	2	[1]	5	[2]	5	[2]
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		645	[6]	658	[6]	1,850	[7]	1,895	[7]
Rate-regulated natural gas revenues		86	[6]	80	[6]	519	[7]	468	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		731	[6]	738	[6]	2,369	[7]	2,363	[7]
Net income (loss)		63		62		242		231
Assets		9,541				9,541				9,104
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		6	[1]	3	[1]	18	[2]	12	[2]
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		1,334	[6],[8]	1,280	[6],[8]	3,549	[7],[9]	3,417	[7],[9]
Rate-regulated natural gas revenues		24	[6],[8]	18	[6],[8]	129	[7],[9]	105	[7],[9]
Shared service and other revenues		3	[6],[8]	12	[6],[8]	10	[7],[9]	35	[7],[9]
Revenues		1,361	[6],[8]	1,310	[6],[8]	3,688	[7],[9]	3,557	[7],[9]
Net income (loss)		187		153		336		359
Assets		21,957				21,957				21,247
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[1]	12	[1]	11	[2]	35	[2]
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		628	[8]	604	[8]	1,708	[9]	1,649	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		628	[8]	604	[8]	1,708	[9]	1,649	[9]
Net income (loss)		89		87		174		188
Assets		8,199				8,199				7,832
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		1		5		4
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		304	[8]	309	[8]	872	[9]	866	[9]
Rate-regulated natural gas revenues		24	[8]	18	[8]	129	[9]	105	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		328	[8]	327	[8]	1,001	[9]	971	[9]
Net income (loss)		33		31		90		107
Assets		4,601				4,601				4,357
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2		6		6
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		406	[8]	370	[8]	981	[9]	915	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		406	[8]	370	[8]	981	[9]	915	[9]
Net income (loss)		61		41		76		77
Assets		3,694				3,694				3,445
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		0		2		2
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Competitive businesses natural gas revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Competitive businesses other revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Rate-regulated electric revenues		0	[10],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Rate-regulated natural gas revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Shared service and other revenues		458	[6],[12]	446	[6],[12]	1,398	[7],[13]	1,316	[7],[13]
Revenues		458	[6],[12]	446	[6],[12]	1,398	[7],[13]	1,316	[7],[13]
Net income (loss)		(69)	[12]	3	[12]	(125)	[13]	58	[13]
Assets	[12]	8,418				8,418				8,618
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		0	[8],[14]	0	[8],[14]	0	[9],[15]	0	[9],[15]
Rate-regulated natural gas revenues		0	[8],[14]	0	[8],[14]	0	[9],[15]	0	[9],[15]
Shared service and other revenues		103	[8],[14]	12	[8],[14]	326	[9],[15]	37	[9],[15]
Revenues		103	[8],[14]	12	[8],[14]	326	[9],[15]	37	[9],[15]
Net income (loss)		1	[14]	(18)	[14]	(15)	[15]	(48)	[15]
Assets	[14]	10,763				10,763				$ 10,600
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		456	[1],[12]	445	[1],[12]	1,392	[2],[13]	1,312	[2],[13]
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		103	[14]	13	[14]	325	[15]	37	[15]
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,456		1,432		4,179		4,222
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		35		31		97		111
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		69		98		198		330
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		46		57		143		209
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		26		47		103		138
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		10		7		21		23
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,449	[16]	1,421	[16]	4,162	[17]	4,207	[17]
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7		11		17		15
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,117		1,038		3,593		3,141
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		122		54		419		77
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,121	[16]	1,049	[16]	3,601	[17]	3,158	[17]
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (4)		$ (11)		$ (8)		(17)
Exelon Consolidations [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[2]							$ 2

[1] 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.

[2] 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.

[3] Exelon’s consolidated assets include $9,804 million and $9,597 million at September 30, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,606 million and $3,618 million at September 30, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 — Variable Interest Entities for additional information.

[4] PHI’s consolidated total assets include $36 million and $41 million at September 30, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $78 million and $102 million at September 30, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 3 — Variable Interest Entities for additional information.

[5] Generation’s consolidated assets include $9,768 million and $9,556 million at September 30, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,528 million and $3,516 million at September 30, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 — Variable Interest Entities for additional information.

[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 three months ended September 30, 2018 and 2017.

[7] 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 nine months ended September 30, 2018 and 2017.

[8] 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 September 30, 2018 and 2017.

[9] 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 nine months ended September 30, 2018 and 2017.

[10] 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 September 30, 2018 include revenue from sales to PECO of $35 million, sales to BGE of $69 million, sales to Pepco of $46 million, sales to DPL of $26 million and sales to ACE of $10 million in the Mid-Atlantic region, and sales to ComEd of $122 million in the Midwest region, which eliminate upon consolidation. For the three months ended September 30, 2017, intersegment revenues for Generation include revenue from sales to PECO of $31 million, sales to BGE of $98 million, sales to Pepco of $57 million, sales to DPL of $47 million and sales to ACE of $7 million in the Mid-Atlantic region, and sales to ComEd of $54 million in the Midwest region, which eliminate upon consolidation.

[11] 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 nine months ended September 30, 2018 include revenue from sales to PECO of $97 million, sales to BGE of $198 million, sales to Pepco of $143 million, sales to DPL of $103 million and sales to ACE of $21 million in the Mid-Atlantic region, and sales to ComEd of $419 million in the Midwest region, which eliminate upon consolidation. For the nine months ended September 30, 2017, intersegment revenues for Generation include revenue from sales to PECO of $111 million, sales to BGE of $330 million, sales to Pepco of $209 million, sales to DPL of $138 million and sales to ACE of $23 million in the Mid-Atlantic region, and sales to ComEd of $77 million in the Midwest region, which eliminate upon consolidation.

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

[13] Other primarily includes Exelon’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.

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

[16] Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.

[17] Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.