Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues		$ 9,477		$ 9,693
Operating revenues from affiliates	[1]	0		0
Depreciation, Depletion and Amortization		1,075		1,091
Operating Expenses		8,262		8,648
Interest Revenue (Expense), Net		403		371
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		1,282		702
Income taxes		310		59
Net income (loss)		966		636
Payments to Acquire Property, Plant, and Equipment		1,873		1,880
Assets	[2]	121,593				$ 119,666
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		1,139		1,151
Rate-regulated natural gas revenues		71		78
Revenues		1,228		1,251
Operating revenues from affiliates		3		4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		122		74
Income taxes		5		9
Net income (loss)		117		65
Payments to Acquire Property, Plant, and Equipment		358		258
Assets	[3]	22,294				21,984
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Revenues		5,296		5,512
Operating revenues from affiliates		317		398
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		652		202
Income taxes		224		9
Net income (loss)		422		186
Payments to Acquire Property, Plant, and Equipment		511		628
Assets	[4]	48,682				47,556
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	4,022		4,118
Competitive businesses natural gas revenues	[5]	878		947
Competitive businesses other revenues	[5]	79		48
Rate-regulated electric revenues	[5]	3,831		3,955
Rate-regulated natural gas revenues	[5]	665		625
Shared service and other revenues	[5]	2		0
Revenues	[5]	9,477		9,693
Net income (loss)		966		636
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	(315)		(391)
Competitive businesses natural gas revenues	[5]	(1)		(8)
Competitive businesses other revenues	[5]	(1)		0
Rate-regulated electric revenues	[5]	(8)		(18)
Rate-regulated natural gas revenues	[5]	(4)		(4)
Shared service and other revenues	[5]	(457)		(455)
Revenues	[5]	(786)		(876)
Operating revenues from affiliates	[1]	(785)		(876)
Depreciation, Depletion and Amortization		0		0
Operating Expenses		(783)		(886)
Interest Revenue (Expense), Net		0		0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		0		0
Income taxes		0		0
Net income (loss)		0		0
Payments to Acquire Property, Plant, and Equipment		0		0
Assets		(10,213)				(9,800)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	(5)		(4)
Rate-regulated natural gas revenues	[6]	1		0
Shared service and other revenues	[6]	(102)		(109)
Revenues	[6]	(106)		(113)
Operating revenues from affiliates		(106)		(113)
Depreciation, Depletion and Amortization		(1)		0
Operating Expenses		(105)		(112)
Interest Revenue (Expense), Net		(1)		1
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		(118)		(69)
Income taxes		0		0
Net income (loss)		4		4
Payments to Acquire Property, Plant, and Equipment		0		0
Assets		(5,478)				(5,421)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5],[7]	4,337		4,509
Competitive businesses natural gas revenues	[5],[7]	879		955
Competitive businesses other revenues	[5],[7]	80		48
Rate-regulated electric revenues	[5],[7]	0		0
Rate-regulated natural gas revenues	[5],[7]	0		0
Shared service and other revenues	[5],[7]	0		0
Revenues	[5],[7]	5,296		5,512
Depreciation, Depletion and Amortization		405		448
Operating Expenses		4,963		5,218
Interest Revenue (Expense), Net		111		101
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		652		202
Income taxes		224		9
Net income (loss)	[7]	422		186
Payments to Acquire Property, Plant, and Equipment		511		628
Assets	[7]	48,682				47,556
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1],[7]	317		400
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5]	1,408		1,512
Rate-regulated natural gas revenues	[5]	0		0
Shared service and other revenues	[5]	0		0
Revenues	[5]	1,408		1,512
Depreciation, Depletion and Amortization		251		228
Operating Expenses		1,135		1,223
Interest Revenue (Expense), Net		87		89
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		197		211
Income taxes		40		46
Net income (loss)		157		165
Payments to Acquire Property, Plant, and Equipment		503		531
Assets		31,582				31,213
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	4		14
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5]	620		634
Rate-regulated natural gas revenues	[5]	280		232
Shared service and other revenues	[5]	0		0
Revenues	[5]	900		866
Depreciation, Depletion and Amortization		81		75
Operating Expenses		678		724
Interest Revenue (Expense), Net		33		33
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		193		111
Income taxes		25		(2)
Net income (loss)		168		113
Payments to Acquire Property, Plant, and Equipment		222		217
Assets		10,956				10,642
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	1		2
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5]	658		658
Rate-regulated natural gas revenues	[5]	318		319
Shared service and other revenues	[5]	0		0
Revenues	[5]	976		977
Depreciation, Depletion and Amortization		136		134
Operating Expenses		756		800
Interest Revenue (Expense), Net		29		25
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		196		156
Income taxes		36		28
Net income (loss)		160		128
Payments to Acquire Property, Plant, and Equipment		258		224
Assets		9,967				9,716
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	6		6
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0		0
Competitive businesses natural gas revenues	[5]	0		0
Competitive businesses other revenues	[5]	0		0
Rate-regulated electric revenues	[5],[6]	1,153		1,169
Rate-regulated natural gas revenues	[5],[6]	71		78
Shared service and other revenues	[5],[6]	4		4
Revenues	[5],[6]	1,228		1,251
Depreciation, Depletion and Amortization		180		183
Operating Expenses		1,054		1,125
Interest Revenue (Expense), Net		65		63
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		122		74
Income taxes		5		9
Net income (loss)		117		65
Payments to Acquire Property, Plant, and Equipment		358		258
Assets		22,294				21,984
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	4		4
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	575		557
Rate-regulated natural gas revenues	[6]	0		0
Shared service and other revenues	[6]	0		0
Revenues	[6]	575		557
Depreciation, Depletion and Amortization		94		96
Operating Expenses		491		501
Interest Revenue (Expense), Net		34		31
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		57		33
Income taxes		2		2
Net income (loss)		55		31
Payments to Acquire Property, Plant, and Equipment		144		127
Assets		8,420				8,299
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	310		306
Rate-regulated natural gas revenues	[6]	70		78
Shared service and other revenues	[6]	0		0
Revenues	[6]	380		384
Depreciation, Depletion and Amortization		46		45
Operating Expenses		308		335
Interest Revenue (Expense), Net		15		13
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		60		38
Income taxes		7		7
Net income (loss)		53		31
Payments to Acquire Property, Plant, and Equipment		78		65
Assets		4,660				4,588
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6]	273		310
Rate-regulated natural gas revenues	[6]	0		0
Shared service and other revenues	[6]	0		0
Revenues	[6]	273		310
Depreciation, Depletion and Amortization		31		33
Operating Expenses		252		287
Interest Revenue (Expense), Net		14		16
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		10		8
Income taxes		0		1
Net income (loss)		10		7
Payments to Acquire Property, Plant, and Equipment		128		63
Assets		3,783				3,699
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		1
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5],[8]	0		0
Competitive businesses natural gas revenues	[5],[8]	0		0
Competitive businesses other revenues	[5],[8]	0		0
Rate-regulated electric revenues	[8]	0	[7]	0	[5]
Rate-regulated natural gas revenues	[5],[8]	0		0
Shared service and other revenues	[5],[8]	455		451
Revenues	[5],[8]	455		451
Depreciation, Depletion and Amortization	[8]	22		23
Operating Expenses	[8]	459		444
Interest Revenue (Expense), Net	[8]	78		60
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	[8]	(78)		(52)
Income taxes	[8]	(20)		(31)
Net income (loss)	[8]	(58)		(21)
Payments to Acquire Property, Plant, and Equipment	[8]	21		22
Assets	[8]	8,325				8,355
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[6],[9]	0		0
Rate-regulated natural gas revenues	[6],[9]	0		0
Shared service and other revenues	[6],[9]	106		113
Revenues	[6],[9]	106		113
Depreciation, Depletion and Amortization		10		9
Operating Expenses		108		114
Interest Revenue (Expense), Net		3		2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest		113		64
Income taxes		(4)		(1)
Net income (loss)	[9]	(5)		(8)
Payments to Acquire Property, Plant, and Equipment		8		3
Assets		10,909				$ 10,819
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1],[8]	453		450
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[9]	105		112
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,256		1,440
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		45		37
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		76		65
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		70		52
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		23		46
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		8		6
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[10]	1,262		1,435
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(6)		5
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,108		1,346
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		94		194
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[10]	1,114		1,344
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (6)		$ 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] Exelon’s consolidated assets include $9,546 million and $9,667 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,572 million and $3,548 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2 — Variable Interest Entities for additional information.

[3] PHI’s consolidated total assets include $31 million and $33 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $64 million and $69 million at March 31, 2019 and December 31, 2018, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 — Variable Interest Entities for additional information.

[4] Generation’s consolidated assets include $9,515 million and $9,634 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,508 million and $3,480 million at March 31, 2019 and December 31, 2018, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2 — Variable Interest Entities for additional information.

[5] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.

[6] ncludes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 17 — Supplemental Financial Information for additional information on total utility taxes.

[7] Intersegment revenues for Generation in 2019 include revenue from sales to PECO of $45 million, sales to BGE of $76 million, sales to Pepco of $70 million, sales to DPL of $23 million and sales to ACE of $8 million in the Mid-Atlantic region, and sales to ComEd of $94 million in the Midwest region, which eliminate upon consolidation. Intersegment revenues for Generation in 2018 include revenue from sales to PECO of $37 million, sales to BGE of $65 million, sales to Pepco of $52 million, sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation.

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

[9] ther primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities.The following tables disaggregate the Registrants' revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. For Generation, the disaggregation of revenues reflects Generation’s two primary products of power sales and natural gas sales, with further disaggregation of power sales provided by geographic region. For the Utility Registrants, the disaggregation of revenues reflects the two primary utility services of rate-regulated electric sales and rate-regulated natural gas sales (where applicable), with further disaggregation of these tariff sales provided by major customer groups. Exelon’s disaggregated revenues are consistent with Generation and the Utility Registrants, but exclude any intercompany revenues.Competitive Business Revenues (Generation):

[10] des all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.(b)