No definition available.

Name:	exc_IncomeTaxesLineItems
Namespace Prefix:	exc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.7)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_CurrentIncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.7)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_DeferredIncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

+ Details

Name:	us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount deducted from an entities' taxes, reflecting a percentage of an amount invested in certain assets spread over the useful life of those assets; includes deferred investment tax credits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

Name:	us-gaap_InvestmentTaxCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=exc_ExelonGenerationCoLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_CommonwealthEdisonCoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_PecoEnergyCoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_BaltimoreGasAndElectricCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_PotomacElectricPowerCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_DelmarvaPowerandLightCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_AtlanticCityElectricCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_PepcoHoldingsLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_SuccessorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_PredecessorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_InternalRevenueServiceIRSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_StateAndLocalJurisdictionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (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
Income Taxes [Line Items]
Income taxes			$ (125)	$ 761	$ 1,073
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes			(1,375)	290	502
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes			417	301	280
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes			104	149	143
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income taxes			218	174	189
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income taxes			105	41	102
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Income taxes			71	22	49
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income taxes			26	(4)	33
Pepco Holdings LLC [Member] \| Successor [Member]
Income Taxes [Line Items]
Income taxes		$ 3	217
Pepco Holdings LLC [Member] \| Predecessor [Member]
Income Taxes [Line Items]
Income taxes	$ 17				163
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current			194	60	407
Deferred			(469)	607	566
Investment Tax Credit			(25)	(24)	(22)
Internal Revenue Service (IRS) [Member] \| Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current			584	513	546
Deferred			(2,003)	(247)	16
Investment Tax Credit			(21)	(20)	(19)
Internal Revenue Service (IRS) [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current			(191)	(135)	(80)
Deferred			523	379	310
Investment Tax Credit			(2)	(2)	(2)
Internal Revenue Service (IRS) [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Current			71	63	64
Deferred			28	72	69
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current			74	51	25
Deferred			101	88	126
Investment Tax Credit			(1)	(1)	(1)
Internal Revenue Service (IRS) [Member] \| Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current			(20)	(118)	(54)
Deferred			114	136	126
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] \| Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Current			(24)	(88)	(27)
Deferred			82	97	73
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] \| Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current			(12)	(26)	(2)
Deferred			34	22	27
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] \| Pepco Holdings LLC [Member] \| Successor [Member]
Income Taxes [Line Items]
Current		(281)	(60)
Deferred		283	250
Investment Tax Credit		(1)	(1)
Internal Revenue Service (IRS) [Member] \| Pepco Holdings LLC [Member] \| Predecessor [Member]
Income Taxes [Line Items]
Current	0				12
Deferred	10				103
Investment Tax Credit	0				(1)
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current			14	39	(86)
Deferred			161	79	208
State and Local Jurisdiction [Member] \| Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current			65	45	(90)
Deferred			0	(1)	49
State and Local Jurisdiction [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current			(49)	(4)	7
Deferred			136	63	45
State and Local Jurisdiction [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Current			14	9	(10)
Deferred			(9)	5	20
State and Local Jurisdiction [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current			(5)	5	0
Deferred			49	31	39
State and Local Jurisdiction [Member] \| Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current			(2)	7	6
Deferred			13	16	24
State and Local Jurisdiction [Member] \| Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Current			0	1	2
Deferred			13	12	1
State and Local Jurisdiction [Member] \| Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current			0	0	3
Deferred			4	$ 0	5
State and Local Jurisdiction [Member] \| Pepco Holdings LLC [Member] \| Successor [Member]
Income Taxes [Line Items]
Current		(11)	(4)
Deferred		$ 13	$ 32
State and Local Jurisdiction [Member] \| Pepco Holdings LLC [Member] \| Predecessor [Member]
Income Taxes [Line Items]
Current	0				17
Deferred	$ 7				$ 32