Segment Information Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended		12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				$ 14,195		$ 13,960		$ 15,200
Competitive businesses natural gas revenues	[1]				2,575		2,146		2,433
Competitive businesses other revenues	[1]				590		211		757
Rate-regulated electric revenues	[1]				14,840		13,869		9,876
Rate-regulated natural gas revenues	[1]				1,333		1,166		1,176
Shared service and other revenues	[1]				0		7		5
Operating revenues from affiliates					7		10		9
Depreciation and amortization					3,828		3,936		2,450
Operating Expenses	[1]				29,720		28,200		25,056
Equity in losses of unconsolidated affiliates					(32)		(24)		(7)
Interest expense, net					1,560		1,536		1,033
Income (loss) before income taxes					3,756		1,989		3,330
Income taxes					(125)		761		1,073
Net Income (Loss)					3,849		1,204		2,250
Capital expenditures					7,584		8,553		7,624
Assets	[2]		$ 114,904		116,700		114,904
Predecessor [Member]
Segment Reporting Information [Line Items]
Equity in losses of unconsolidated affiliates									0
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					1,115		1,439		749
Equity in losses of unconsolidated affiliates									(8)
Income (loss) before income taxes					1,429		873		1,850
Income taxes					(1,375)		290		502
Net Income (Loss)					2,771		558		1,340
Capital expenditures					2,259		3,078		3,841
Assets	[3]		46,974		48,387		46,974
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[4]				121		47		18
PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[5]				1		1		1
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]				138		290		224
Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[5]				4		4		4
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[7]				388		608		502
Potomac Electric Power Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					255	[8]	295	[9]	0	[8]
Delmarva Power and Light Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					179	[10]	154	[8]	0	[10]
Atlantic City Electric Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					29	[9]	37	[10]	0	[9]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				(1,105)		(1,430)		(744)
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				(1)		(4)		(1)
Rate-regulated electric revenues	[1]				(29)		(31)		(5)
Rate-regulated natural gas revenues	[1]				(10)		(13)		(15)
Shared service and other revenues	[1]				(1,880)		(1,686)		(1,367)
Operating revenues from affiliates	[11]				2		5		5
Depreciation and amortization					0		0		0
Operating Expenses	[1]				(3,026)		(3,164)		(2,131)
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					0		0		0
Income (loss) before income taxes					(2)		(5)		(5)
Income taxes					0		0		0
Net Income (Loss)					(2)		(5)		(5)
Capital expenditures					0		0		0
Assets			(11,334)		(10,552)		(11,334)
Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		(13)		(14)
Rate-regulated natural gas revenues	[12]		0		0
Shared service and other revenues	[12]		0		(3)
Operating revenues from affiliates			(13)		(19)
Depreciation and amortization			0		(1)
Operating Expenses			(13)		(17)
Interest expense, net			0		(1)
Income (loss) before income taxes			71		(404)
Income taxes			0		0
Net Income (Loss)			45		50
Capital expenditures			0		0
Assets			(4,724)		(4,987)		(4,724)
Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	$ (4)							(2)
Rate-regulated natural gas revenues	[12]	0							0
Shared service and other revenues	[12]	0							0
Operating revenues from affiliates		(4)							(15)
Depreciation and amortization		(4)							0
Operating Expenses		(3)							0
Interest expense, net		(2)							(1)
Income (loss) before income taxes		(118)							(29)
Income taxes		0							27
Net Income (Loss)		0							(1)
Capital expenditures		0							0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[13]				15,300		15,390		15,944
Competitive businesses natural gas revenues	[1],[13]				2,575		2,146		2,433
Competitive businesses other revenues	[1],[13]				591		215		758
Rate-regulated electric revenues	[1],[13]				0		0		0
Rate-regulated natural gas revenues	[1],[13]				0		0		0
Shared service and other revenues	[1],[13]				0		0		0
Depreciation and amortization	[13]				1,457		1,879		1,054
Operating Expenses	[1],[13]				17,993		16,856		16,872
Equity in losses of unconsolidated affiliates	[13]				(33)		(25)		(8)
Interest expense, net	[13]				440		364		365
Income (loss) before income taxes	[13]				1,429		873		1,850
Income taxes	[13]				(1,375)		290		502
Net Income (Loss)	[13]				2,771		558		1,340
Capital expenditures	[13]				2,259		3,078		3,841
Assets	[13]		46,974		48,387		46,974
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11],[13]				1,110		1,428		745
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				0		0		0
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				0		0		0
Rate-regulated electric revenues	[1]				5,536		5,254		4,905
Rate-regulated natural gas revenues	[1]				0		0		0
Shared service and other revenues	[1]				0		0		0
Depreciation and amortization					850		775		707
Operating Expenses	[1]				4,214		4,056		3,889
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					361		461		332
Income (loss) before income taxes					984		679		706
Income taxes					417		301		280
Net Income (Loss)					567		378		426
Capital expenditures					2,250		2,734		2,398
Assets			28,335		29,726		28,335
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				15		15		4
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				0		0		0
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				0		0		0
Rate-regulated electric revenues	[1]				2,375		2,531		2,486
Rate-regulated natural gas revenues	[1]				495		463		546
Shared service and other revenues	[1]				0		0		0
Depreciation and amortization					286		270		260
Operating Expenses	[1]				2,215		2,292		2,404
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					126		123		114
Income (loss) before income taxes					538		587		521
Income taxes					104		149		143
Net Income (Loss)					434		438		378
Capital expenditures					732		686		601
Assets			10,831		10,170		10,831
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				7		8		2
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				0		0		0
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				0		0		0
Rate-regulated electric revenues	[1]				2,489		2,609		2,490
Rate-regulated natural gas revenues	[1]				687		624		645
Shared service and other revenues	[1]				0		0		0
Depreciation and amortization					473		423		366
Operating Expenses	[1]				2,562		2,683		2,578
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					105		103		99
Income (loss) before income taxes					525		468		477
Income taxes					218		174		189
Net Income (Loss)					307		294		288
Capital expenditures					882		934		719
Assets			8,704		9,104		8,704
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				16		21		14
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[14]		0		0				0
Competitive businesses natural gas revenues	[1],[14]		0		0				0
Competitive businesses other revenues	[1],[14]		0		0				0
Rate-regulated electric revenues	[1],[14]		3,506	[12]	4,469	[12]			0
Rate-regulated natural gas revenues	[1],[14]		92	[12]	161	[12]			0
Shared service and other revenues	[1],[14]		45	[12]	49	[12]			0
Depreciation and amortization	[14]		515		675				0
Operating Expenses	[1],[14]		3,549		3,911				0
Equity in losses of unconsolidated affiliates	[14]		0		0				0
Interest expense, net	[14]		195		245				0
Income (loss) before income taxes	[14]		(58)		578				0
Income taxes	[14]		3		217				0
Net Income (Loss)	[14]		(61)		362				0
Capital expenditures	[14]		1,008		1,396				0
Assets	[14]		21,025		21,247		21,025
Pepco Holdings LLC [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	1,096							4,770
Rate-regulated natural gas revenues	[12]	57							165
Shared service and other revenues	[12]	0							0
Depreciation and amortization		152							624
Operating Expenses		1,048							4,308
Interest expense, net		65							280
Income (loss) before income taxes		36							481
Income taxes		17							163
Net Income (Loss)		19							327
Capital expenditures		273							1,230
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11],[14]		45		50				0
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0							0
Potomac Electric Power Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		1,675		2,158
Rate-regulated natural gas revenues	[12]		0		0
Shared service and other revenues	[12]		0		0
Depreciation and amortization			224		321
Operating Expenses			1,577		1,760
Interest expense, net			98		121
Income (loss) before income taxes			36		310
Income taxes			26		105
Net Income (Loss)			10		205
Capital expenditures			489		628
Assets			7,335		7,832		7,335
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	511							2,129
Rate-regulated natural gas revenues	[12]	0							0
Shared service and other revenues	[12]	0							0
Depreciation and amortization		71							256
Operating Expenses		443							1,790
Interest expense, net		29							124
Income (loss) before income taxes		47							289
Income taxes		15							102
Net Income (Loss)		32							187
Capital expenditures		97							544
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			4		6
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1							5
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		850		1,139
Rate-regulated natural gas revenues	[12]		92		161
Shared service and other revenues	[12]		0		0
Depreciation and amortization			120		167
Operating Expenses			952		1,071
Interest expense, net			38		51
Income (loss) before income taxes			(30)		192
Income taxes			5		71
Net Income (Loss)			(35)		121
Capital expenditures			277		428
Assets			4,153		4,357		4,153
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	279							1,138
Rate-regulated natural gas revenues	[12]	56							164
Shared service and other revenues	[12]	0							0
Depreciation and amortization		37							148
Operating Expenses		284							1,137
Interest expense, net		12							50
Income (loss) before income taxes		43							125
Income taxes		17							49
Net Income (Loss)		26							76
Capital expenditures		72							352
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			5		8
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2							6
Atlantic City Electric Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		989		1,186
Rate-regulated natural gas revenues	[12]		0		0
Shared service and other revenues	[12]		0		0
Depreciation and amortization			128		146
Operating Expenses			1,000		1,029
Interest expense, net			47		61
Income (loss) before income taxes			(51)		103
Income taxes			(5)		26
Net Income (Loss)			(47)		77
Capital expenditures			218		312
Assets			3,457		3,445		3,457
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	268							1,295
Rate-regulated natural gas revenues	[12]	0							0
Shared service and other revenues	[12]	0							0
Depreciation and amortization		37							175
Operating Expenses		251							1,161
Interest expense, net		15							64
Income (loss) before income taxes		5							73
Income taxes		1							33
Net Income (Loss)		5							40
Capital expenditures		93							300
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			2		2
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1							4
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[15]				0		0		0
Competitive businesses natural gas revenues	[1],[15]				0		0		0
Competitive businesses other revenues	[1],[15]				0		0		0
Rate-regulated electric revenues	[1],[15]				0		0		0
Rate-regulated natural gas revenues	[1],[15]				0		0		0
Shared service and other revenues	[1],[15]				1,831		1,648		1,372
Depreciation and amortization	[15]				87		74		63
Operating Expenses	[1],[15]				1,851		1,928		1,444
Equity in losses of unconsolidated affiliates	[15]				1		1		1
Interest expense, net	[15]				283		290		123
Income (loss) before income taxes	[15]				(296)		(555)		(219)
Income taxes	[15]				294		(156)		(41)
Net Income (Loss)	[15]				(590)		(398)		(177)
Capital expenditures	[15]				65		113		65
Assets	[15]		10,369		8,618		10,369
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12],[16]		5		0
Rate-regulated natural gas revenues	[12],[16]		0		0
Shared service and other revenues	[12],[16]		45		52
Depreciation and amortization	[16]		43		42
Operating Expenses	[16]		33		68
Interest expense, net	[16]		12		13
Income (loss) before income taxes	[16]		(84)		377
Income taxes	[16]		(23)		15
Net Income (Loss)	[16]		(34)		(91)
Capital expenditures	[16]		24		28
Assets	[16]		10,804		10,600		10,804
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12],[16]	42							210
Rate-regulated natural gas revenues	[12],[16]	1							1
Shared service and other revenues	[12],[16]	0							0
Depreciation and amortization	[16]	11							45
Operating Expenses	[16]	73							220
Interest expense, net	[16]	11							43
Income (loss) before income taxes	[16]	59							23
Income taxes	[16]	(16)							(48)
Net Income (Loss)	[16]	(44)							25
Capital expenditures	[16]	11							34
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11],[15]				1,824		1,647		1,367
Corporate and Other [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[16]		$ 47		53
Corporate and Other [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[16]	$ 0							0
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					25		(33)		(74)
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					(25)		10		(2)
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				$ (3,020)		$ (3,159)		$ (2,127)

[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 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.

[2] Exelon’s consolidated assets include $9,565 million and $8,893 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,612 million and $3,356 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.

[3] Generation’s consolidated assets include $9,524 million and $8,817 million at December 31, 2017 and 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,510 million and $3,170 million at December 31, 2017 and 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.

[4] Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.

[5] The intersegment profit associated with the 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. See Note 3—Regulatory Matters for additional information.

[6] Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. See Note 3—Regulatory Matters for additional information.

[7] Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[8] (d)Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3—Regulatory Matters for additional information.

[9] Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3—Regulatory Matters for additional information.

[10] (e)Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[11] 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.

[12] 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 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.

[13] Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2017, intersegment revenues for Generation include revenue from sales to PECO of $138 million, sales to BGE of $388 million, sales to Pepco of $255 million, sales to DPL of $179 million and sales to ACE of $29 million in the Mid-Atlantic region, and sales to ComEd of $121 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2016, intersegment revenues for Generation include revenue from sales to PECO of $290 million and sales to BGE of $608 million in the Mid-Atlantic region, and sales to ComEd of $47 million in the Midwest region, which eliminate upon consolidation. For the Successor period of March 24, 2016 to December 31, 2016, intersegment revenues for Generation include revenue from sales to Pepco of $295 million, sales to DPL of $154 million and sales to ACE of $37 million in the Mid-Atlantic region, which eliminate upon consolidation. For the year ended December 31, 2015, intersegment revenues for Generation include revenue from sales to PECO of $224 million and sales to BGE of $502 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region, which eliminate upon consolidation.

[14] Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2017. PHI includes the three reportable segments: Pepco, DPL and ACE. See tables below for PHI's predecessor periods, including Pepco, DPL and ACE, for January 1, 2016 to March 23, 2016 and for the year ended December 31, 2015.

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

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