Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended					6 Months Ended		9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Mar. 23, 2016	Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016		Dec. 31, 2016
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		$ 3,747	[1]	$ 3,823	[1]				$ 10,597	[2]	$ 10,559	[2]
Competitive businesses natural gas revenues		460	[1]	326	[1]				1,807	[2]	1,515	[2]
Competitive businesses other revenues		249	[1]	386	[1]				520	[2]	169	[2]
Rate-regulated electric revenues		4,164	[1]	4,330	[1]				11,318	[2]	10,461	[2]
Rate-regulated natural gas revenues		149	[1]	137	[1]				906	[2]	781	[2]
Shared service and other revenues		0	[1]	0	[1]				1	[2]	1	[2]
Operating revenues from affiliates		0	[3]	1	[3]				2	[4]	3	[4]
Net income (loss)		867		526					1,911		956
Assets		118,473							118,473				$ 114,904
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		296		502					894		1,129
Net income (loss)		348		271					491		556
Assets		47,744							47,744				46,974
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		(295)	[1]	(499)	[1]				(888)	[2]	(1,118)	[2]
Competitive businesses natural gas revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses other revenues		0	[1]	(1)	[1]				0	[2]	(2)	[2]
Rate-regulated electric revenues		(7)	[1]	(8)	[1]				(23)	[2]	(24)	[2]
Rate-regulated natural gas revenues		(2)	[1]	(5)	[1]				(6)	[2]	(10)	[2]
Shared service and other revenues		(458)	[1]	(373)	[1]				(1,350)	[2]	(1,199)	[2]
Operating revenues from affiliates		(759)	[3]	(885)	[3]				(2,262)	[4]	(2,351)	[4]
Net income (loss)		0		(1)					(2)		(3)
Assets		(11,286)							(11,286)				(11,334)
Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		(3)	[5]	(4)	[5]		$ (9)	[6]	(13)	[6]
Rate-regulated natural gas revenues		0	[5]	0	[5]		0	[6]	0	[6]
Shared service and other revenues		0	[5]	0	[5]		0	[6]	(2)	[6]
Operating revenues from affiliates		(4)		(4)			(9)		(14)
Net income (loss)		12		11			34		35
Assets		(4,984)							(4,984)				(4,724)
Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]					$ (4)
Rate-regulated natural gas revenues	[6]					0
Shared service and other revenues	[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 businesses electric revenues		4,042	[1],[7]	4,322	[1],[7]				11,485	[2],[8]	11,677	[2],[8]
Competitive businesses natural gas revenues		460	[1],[7]	326	[1],[7]				1,807	[2],[8]	1,515	[2],[8]
Competitive businesses other revenues		249	[1],[7]	387	[1],[7]				520	[2],[8]	171	[2],[8]
Rate-regulated electric revenues		0	[1],[7]	0	[1],[7]				0	[2],[8]	0	[2],[8]
Rate-regulated natural gas revenues		0	[1],[7]	0	[1],[7]				0	[2],[8]	0	[2],[8]
Shared service and other revenues		0	[1],[7]	0	[1],[7]				0	[2],[8]	0	[2],[8]
Net income (loss)		348	[7]	271	[7]				491	[8]	556	[8]
Assets	[7]	47,744							47,744				46,974
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		294	[3],[7]	500	[3],[7]				888	[4],[8]	1,121	[4],[8]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses natural gas revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses other revenues		0	[1]	0	[1]				0	[2]	0	[2]
Rate-regulated electric revenues		1,571	[1]	1,497	[1]				4,227	[2]	4,031	[2]
Rate-regulated natural gas revenues		0	[1]	0	[1]				0	[2]	0	[2]
Shared service and other revenues		0	[1]	0	[1]				0	[2]	0	[2]
Net income (loss)		189		37					447		297
Assets		29,649							29,649				28,335
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[3]	4	[3]				12	[4]	12	[4]
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses natural gas revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses other revenues		0	[1]	0	[1]				0	[2]	0	[2]
Rate-regulated electric revenues		662	[1]	740	[1]				1,802	[2]	1,971	[2]
Rate-regulated natural gas revenues		53	[1]	48	[1]				339	[2]	322	[2]
Shared service and other revenues		0	[1]	0	[1]				0	[2]	0	[2]
Net income (loss)		112		122					327		346
Assets		11,480							11,480				10,831
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	[3]	2	[3]				5	[4]	5	[4]
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses natural gas revenues		0	[1]	0	[1]				0	[2]	0	[2]
Competitive businesses other revenues		0	[1]	0	[1]				0	[2]	0	[2]
Rate-regulated electric revenues		658	[1]	735	[1]				1,895	[2]	1,998	[2]
Rate-regulated natural gas revenues		80	[1]	77	[1]				468	[2]	423	[2]
Shared service and other revenues		0	[1]	0	[1]				0	[2]	0	[2]
Net income (loss)		62		56					231		191
Assets		8,923							8,923				8,704
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[3]	7	[3]				12	[4]	16	[4]
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[1],[9]	0	[1],[9]				0	[2],[10]	0	[2],[10]
Competitive businesses natural gas revenues		0	[1],[9]	0	[1],[9]				0	[2],[10]	0	[2],[10]
Competitive businesses other revenues		0	[1],[9]	0	[1],[9]				0	[2],[10]	0	[2],[10]
Rate-regulated electric revenues		1,280	[1],[5],[9]	1,366	[1],[5],[9]		2,485	[6]	3,417	[2],[6],[10]	2,485	[2],[10]
Rate-regulated natural gas revenues		18	[1],[5],[9]	17	[1],[5],[9]		46	[6]	105	[2],[6],[10]	46	[2],[10]
Shared service and other revenues		12	[1],[5],[9]	11	[1],[5],[9]		34	[6]	35	[2],[6],[10]	34	[2],[10]
Net income (loss)		153	[9]	166	[9]		(91)		359	[10]	(91)	[10]
Assets	[9]	21,301							21,301				21,025
Pepco Holdings LLC [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]					1,096
Rate-regulated natural gas revenues	[6]					57
Shared service and other revenues	[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]	11	[3],[9]		34		35	[4],[10]	34	[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]
Rate-regulated electric revenues		604	[5]	635	[5]		1,184	[6]	1,649	[6]
Rate-regulated natural gas revenues		0	[5]	0	[5]		0	[6]	0	[6]
Shared service and other revenues		0	[5]	0	[5]		0	[6]	0	[6]
Net income (loss)		87		79			(12)		188
Assets		7,775							7,775				7,335
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]					511
Rate-regulated natural gas revenues	[6]					0
Shared service and other revenues	[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		4
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]
Rate-regulated electric revenues		309	[5]	314	[5]		593	[6]	866	[6]
Rate-regulated natural gas revenues		18	[5]	17	[5]		46	[6]	105	[6]
Shared service and other revenues		0	[5]	0	[5]		0	[6]	0	[6]
Net income (loss)		31		44			(42)		107
Assets		4,276							4,276				4,153
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]					279
Rate-regulated natural gas revenues	[6]					56
Shared service and other revenues	[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			4		6
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]
Rate-regulated electric revenues		370	[5]	421	[5]		714	[6]	915	[6]
Rate-regulated natural gas revenues		0	[5]	0	[5]		0	[6]	0	[6]
Shared service and other revenues		0	[5]	0	[5]		0	[6]	0	[6]
Net income (loss)		41		47			(55)		77
Assets		3,510							3,510				3,457
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]					268
Rate-regulated natural gas revenues	[6]					0
Shared service and other revenues	[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		0		1			2		2
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 businesses electric revenues		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Competitive businesses natural gas revenues		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Competitive businesses other revenues		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Rate-regulated electric revenues		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Rate-regulated natural gas revenues		0	[1],[11]	0	[1],[11]				0	[2],[12]	0	[2],[12]
Shared service and other revenues		446	[1],[11]	362	[1],[11]				1,316	[2],[12]	1,166	[2],[12]
Net income (loss)		3	[11]	(125)	[11]				58	[12]	(340)	[12]
Assets	[11]	10,662							10,662				10,369
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		0	[5],[13]	0	[5],[13]		3	[6],[14]	0	[6],[14]
Rate-regulated natural gas revenues		0	[5],[13]	0	[5],[13]		0	[6],[14]	0	[6],[14]
Shared service and other revenues		12	[5],[13]	11	[5],[13]		34	[6],[14]	37	[6],[14]
Net income (loss)		(18)	[13]	(15)	[13]		(16)	[14]	(48)	[14]
Assets	[13]	10,724							10,724				$ 10,804
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6],[14]					42
Rate-regulated natural gas revenues	[6],[14]					1
Shared service and other revenues	[6],[14]					0
Net income (loss)	[14]					(44)
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		445	[3],[11]	362	[3],[11]				1,312	[4],[12]	1,166	[4],[12]
Corporate and Other [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		13	[13]	11	[13]		35	[14]	37	[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		31		91					111		234
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		98		183					330		489
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		57		128			223		209
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		47		63			109		138
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7		15			$ 28		23
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		11		(13)					15		(40)
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		54		20					77		38
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (11)		$ 1					$ (17)		$ 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 19 — Supplemental Financial Information for total utility taxes for the three months ended September 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 19 — Supplemental Financial Information for total utility taxes for the nine months ended September 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 19 — Supplemental Financial Information for total utility taxes for the three months ended September 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 19 — Supplemental Financial Information for total utility taxes for the nine months ended September 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 September 30, 2017 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. For the three months ended September 30, 2016, intersegment revenues for Generation include revenue from sales to PECO of $91 million, sales to BGE of $183 million, sales to Pepco of $128 million, sales to DPL of $63 million, and sales to ACE of $15 million in the Mid-Atlantic region, and sales to ComEd of $20 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 nine months ended September 30, 2017 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. For the nine months ended September 30, 2016, intersegment revenues for Generation include revenue from sales to PECO of $234 million and sales to BGE of $489 million in the Mid-Atlantic region, and sales to ComEd of $38 million in the Midwest region. For the Successor period of March 24, 2016 to September 30, 2016, intersegment revenues for Generation include revenue from sales to Pepco of $223 million, sales to DPL of $109 million, and sales to ACE of $28 million in the Mid-Atlantic region.

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

[10] Amounts included represent activity for PHI's successor period, nine months ended September 30, 2017 and March 24, 2016 through September 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.