Cash collateral held related to credit risk.

No definition available.

Name:	exc_CashCollateralHeld
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Cash collateral posted related to credit risk.

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Credit exposure under off system sales

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of receivables due from a electric and gas entity that is affiliated with the reporting entity by means of direct or indirect ownership, due within 1 year (or 1 business cycle).

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of receivables due from a electric entity that is affiliated with the reporting entity by means of direct or indirect ownership, due within 1 year (or 1 business cycle).

+ References

No definition available.

+ Details

Name:	exc_DueFromAffiliateCurrentElectricUtility
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The expected/target percentage of future gas purchases being hedged at a gas distribution company. The percentage is calculated as the amount of hedging products divided by the planned natural gas purchases in support of projected firm sales.

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percent for the expected/target percentage of future generation being hedged at an electric generation company in the next twelve months. The percentage of expected generation hedged is calculated as the amount of equivalent sales divided by the expected generation. Expected generation represents the amount of energy estimated to be generated or purchased through owned or contracted capacity. Equivalent sales represent all hedging products, which include cash-flow hedges, other derivatives and certain non-derivative contracts including sales to affiliates to serve their retail load.

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percent for the expected/target percentage of future generation being hedged at an electric generation company in year three. The percentage of expected generation hedged is calculated as the amount of equivalent sales divided by the expected generation. Expected generation represents the amount of energy estimated to be generated or purchased through owned or contracted capacity. Equivalent sales represent all hedging products, which include cash-flow hedges, other derivatives and certain non-derivative contracts including sales to affiliates to serve their retail load.

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percent for the expected/target percentage of future generation being hedged at an electric generation company in year two. The percentage of expected generation hedged is calculated as the amount of equivalent sales divided by the expected generation. Expected generation represents the amount of energy estimated to be generated or purchased through owned or contracted capacity. Equivalent sales represent all hedging products, which include cash-flow hedges, other derivatives and certain non-derivative contracts including sales to affiliates to serve their retail load.

+ References

No definition available.

+ Details

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Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Incremental collateral amount required to be provided related to its financial instruments, including derivatives, non-derivatives, normal purchase normal sales contracts and applicable payables and receivables, if the credit rating is downgraded below investment grade.

+ References

No definition available.

+ Details

Name:	exc_IncrementalCollateralForLossOfInvestmentGradeCreditRating
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Letters of credit held related to credit risk

+ References

No definition available.

+ Details

Name:	exc_LettersOfCreditHeld
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Letters of credit posted related to credit risk.

+ References

No definition available.

+ Details

Name:	exc_LettersOfCreditPosted
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Revenue related to brokering natural gas. The entity realizes brokered margin as a result of buying and selling natural gas in back-to-back transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 24
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-SubTopic 235
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-Paragraph 23
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62136-109447

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Description of the nature of assets held either as collateral or by third parties that, upon the occurrence of specified triggering event or condition under the credit derivative, the seller can obtain and liquidate to recover amounts paid under the credit derivative.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5708775-113959

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
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-Publisher FASB
-Name Accounting Standards Codification
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-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226016-175313

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Paragraph 10
-Subparagraph (a)
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-SubTopic 10
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-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value as of the balance sheet date of all derivative assets designated as interest rate fair value hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- Details

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- Details

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Name:	dei_LegalEntityAxis=exc_PecoEnergyCoMember
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- Details

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Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative [Line Items]
Ineffective portion recognized in income	$ 0	$ 4,000	$ 9,000	$ 11,000
Cash Collateral Posted	4,000		4,000
Letters of credit posted	34,000		34,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions	23,000		23,000		$ 4,000
Cash Collateral Posted	255,000		255,000		497,000
Letters of credit held	48,000		48,000		33,000
Letters of credit posted	283,000		283,000		293,000
Cash collateral held	20,000		20,000		35,000
Incremental collateral for loss of investment grade credit rating	1,800,000		1,800,000		1,800,000
Interest Rate Fair Value Hedge Asset at Fair Value	19,000		19,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	8,000		8,000
Credit Exposure Under Off System Sales	2,000		$ 2,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged			20.00%
Incremental collateral for loss of investment grade credit rating	22,000		$ 22,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	31,000		31,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	10,000		$ 10,000
Minimum [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months			98.00%
Expected Generation Hedged In Year Two			82.00%
Expected generation hedged in year three			48.00%
Minimum [Member] \| Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged			10.00%
Maximum [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months			101.00%
Expected Generation Hedged In Year Two			85.00%
Expected generation hedged in year three			51.00%
Maximum [Member] \| Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged			20.00%
Other Contract [Member] \| Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties			19
Energy Related Derivative [Member] \| Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties			6
Energy Related Derivative [Member] \| Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue			$ 2,750
Renewable Energy Program [Member] \| Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties			20
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	9,000		$ 9,000		5,000
InterestRateAndForeignExchangeContract [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	19,000		19,000		2,000
Commonwealth Edison Co Affiliate [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	47,000		47,000
PECO Energy Co Affiliate [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	26,000		26,000
Baltimore Gas And Electric Company Affiliate [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	23,000		23,000
Potomac Electric Power Company [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	39,000		39,000
Delmarva Power and Light Company [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	8,000		8,000
Atlantic City Electric Company [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	$ 6,000		$ 6,000
Designated as Hedging Instrument [Member] \| InterestRateAndForeignExchangeContract [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net					1,000
Corporate, Non-Segment [Member] \| Designated as Hedging Instrument [Member] \| InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net					$ 3,000