Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Rate-regulated electric revenues				$ 0				$ 0
Rate-regulated natural gas revenues				0				0
Revenues		$ 8,076		7,665		$ 17,769		16,413
Operating revenues from affiliates		0	[1]	0	[1]	0	[2]	0	[2]
Net income (loss)		542		94		1,179		1,066
Assets	[3]	117,249				117,249				$ 116,770
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		1,052		1,032		2,202		2,100
Rate-regulated natural gas revenues		28		22		106		87
Revenues		1,076		1,074		2,327		2,248
Operating revenues from affiliates		3		12		7		23
Net income (loss)		84		66		149		205
Assets	[4]	21,766				21,766				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		4,579		4,216		10,090		9,093
Operating revenues from affiliates		273		268		671		598
Net income (loss)		181		(236)		368		164
Assets	[5]	47,668				47,668				48,457
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		3,669	[6]	3,493	[6]	7,785	[7]	6,875	[7]
Competitive businesses natural gas revenues		489	[6]	430	[6]	1,436	[7]	1,348	[7]
Competitive businesses other revenues		147	[6]	27	[6]	196	[7]	277	[7]
Rate-regulated electric revenues		3,542	[6]	3,511	[6]	7,496	[7]	7,156	[7]
Rate-regulated natural gas revenues		230	[6]	204	[6]	855	[7]	757	[7]
Shared service and other revenues		(1)	[6]	0	[6]	1	[7]	0	[7]
Revenues		8,076	[6]	7,665	[6]	17,769	[7]	16,413	[7]
Net income (loss)		542		94		1,179		1,066
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		(270)	[6]	(266)	[6]	(663)	[7]	(592)	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	(8)	[7]	0	[7]
Competitive businesses other revenues		(4)	[6]	0	[6]	(2)	[7]	(1)	[7]
Rate-regulated electric revenues		(9)	[6]	(7)	[6]	(27)	[7]	(16)	[7]
Rate-regulated natural gas revenues		(5)	[6]	(1)	[6]	(9)	[7]	(4)	[7]
Shared service and other revenues		(491)	[6]	(461)	[6]	(946)	[7]	(893)	[7]
Revenues		(779)	[6]	(735)	[6]	(1,655)	[7]	(1,506)	[7]
Operating revenues from affiliates		(776)	[1]	(734)	[1]	(1,650)	[2]	(1,503)	[2]
Net income (loss)		0		0		0		0
Assets		(10,655)				(10,655)				(10,552)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		(4)	[8]	(4)	[8]	(8)	[9]	(9)	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		(105)	[8]	(1)	[8]	(214)	[9]	(2)	[9]
Revenues		(109)	[8]	(5)	[8]	(222)	[9]	(11)	[9]
Operating revenues from affiliates		(109)		(5)		(222)		(9)
Net income (loss)		3		12		7		23
Assets		(5,251)				(5,251)				(4,987)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		3,939	[6],[10]	3,759	[6],[10]	8,448	[7],[11]	7,467	[7],[11]
Competitive businesses natural gas revenues		489	[6],[10]	430	[6],[10]	1,444	[7],[11]	1,348	[7],[11]
Competitive businesses other revenues		151	[6],[10]	27	[6],[10]	198	[7],[11]	278	[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		4,579	[6],[10]	4,216	[6],[10]	10,090	[7],[11]	9,093	[7],[11]
Net income (loss)		181	[10]	(236)	[10]	368	[11]	164	[11]
Assets	[10]	47,668				47,668				48,457
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		273	[1],[10]	266	[1],[10]	672	[2],[11]	594	[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		1,398	[6]	1,357	[6]	2,910	[7]	2,656	[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		1,398	[6]	1,357	[6]	2,910	[7]	2,656	[7]
Net income (loss)		164		118		329		259
Assets		30,446				30,446				29,726
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		5	[1]	3	[1]	19	[2]	9	[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		560	[6]	550	[6]	1,193	[7]	1,140	[7]
Rate-regulated natural gas revenues		93	[6]	80	[6]	325	[7]	286	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		653	[6]	630	[6]	1,518	[7]	1,426	[7]
Net income (loss)		96		88		210		215
Assets		10,345				10,345				10,170
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	[1]	2	[1]	3	[2]	3	[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		548	[6]	571	[6]	1,206	[7]	1,237	[7]
Rate-regulated natural gas revenues		114	[6]	103	[6]	433	[7]	388	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		662	[6]	674	[6]	1,639	[7]	1,625	[7]
Net income (loss)		51		45		179		169
Assets		9,241				9,241				9,104
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		6	[1]	3	[1]	12	[2]	8	[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		1,045	[6],[8]	1,040	[6],[8]	2,214	[7],[9]	2,138	[7],[9]
Rate-regulated natural gas revenues		28	[6],[8]	22	[6],[8]	106	[7],[9]	87	[7],[9]
Shared service and other revenues		3	[6],[8]	12	[6],[8]	7	[7],[9]	23	[7],[9]
Revenues		1,076	[6],[8]	1,074	[6],[8]	2,327	[7],[9]	2,248	[7],[9]
Net income (loss)		84		66		149		205
Assets		21,766				21,766				21,247
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[1]	12	[1]	7	[2]	23	[2]
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		523	[8]	514	[8]	1,080	[9]	1,045	[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		523	[8]	514	[8]	1,080	[9]	1,045	[9]
Net income (loss)		54		43		85		101
Assets		8,123				8,123				7,832
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		1		3		3
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		261	[8]	260	[8]	567	[9]	557	[9]
Rate-regulated natural gas revenues		28	[8]	22	[8]	106	[9]	87	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		289	[8]	282	[8]	673	[9]	644	[9]
Net income (loss)		26		19		57		76
Assets		4,562				4,562				4,357
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2		4		4
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		265	[8]	270	[8]	575	[9]	544	[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		265	[8]	270	[8]	575	[9]	544	[9]
Net income (loss)		8		8		15		36
Assets		3,619				3,619				3,445
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		1		2		1
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]	1	[7],[13]
Rate-regulated natural gas revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Shared service and other revenues		487	[6],[12]	449	[6],[12]	940	[7],[13]	870	[7],[13]
Revenues		487	[6],[12]	449	[6],[12]	940	[7],[13]	871	[7],[13]
Net income (loss)		(34)	[12]	13	[12]	(56)	[13]	54	[13]
Assets	[12]	8,438				8,438				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]	1	[9],[15]
Rate-regulated natural gas revenues		0	[8],[14]	0	[8],[14]	0	[9],[15]	0	[9],[15]
Shared service and other revenues		108	[8],[14]	13	[8],[14]	221	[9],[15]	25	[9],[15]
Revenues		108	[8],[14]	13	[8],[14]	221	[9],[15]	26	[9],[15]
Net income (loss)		(7)	[14]	(16)	[14]	(15)	[15]	(31)	[15]
Assets	[14]	10,713				10,713				$ 10,600
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		487	[1],[12]	448	[1],[12]	937	[2],[13]	866	[2],[13]
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		107	[14]	13	[14]	220	[15]	24	[15]
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,282		1,365		2,722		2,790
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		25		34		61		79
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		63		99		128		233
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		46		68		98		152
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		30		40		76		91
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		6		7		12		16
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,278	[16]	1,356	[16]	2,712	[17]	2,785	[17]
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		4		9		10		5
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,130		1,050		2,475		2,102
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		103		18		297		23
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,135	[16]	1,058	[16]	2,479	[17]	2,107	[17]
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (5)		$ (8)		$ (4)		$ (5)

[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 $9,612 million and $9,597 million at June 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 $3,544 million and $3,618 million at June 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 $37 million and $41 million at June 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 $88 million and $102 million at June 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 $9,575 million and $9,556 million at June 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 $3,456 million and $3,516 million at June 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 June 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 six months ended June 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 June 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 six months ended June 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 June 30, 2018 include revenue from sales to PECO of $25 million, sales to BGE of $63 million, sales to Pepco of $46 million, sales to DPL of $30 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $103 million in the Midwest region, which eliminate upon consolidation. For the three months ended June 30, 2017, intersegment revenues for Generation 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, 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 six months ended June 30, 2018 include revenue from sales to PECO of $61 million, sales to BGE of $128 million, sales to Pepco of $98 million, sales to DPL of $76 million and sales to ACE of $12 million in the Mid-Atlantic region, and sales to ComEd of $297 million in the Midwest region, which eliminate upon consolidation. For the six months ended June 30, 2017, intersegment revenues for Generation 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, 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.