Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details)	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted	$ 214,000,000	$ 76,000,000
Fair Value, Inputs, Level 3 [Member] \| Economic Hedges [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	558,000,000	443,000,000
Fair Value, Inputs, Level 3 [Member] \| Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ (301,000,000)	$ (249,000,000)
Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	900.00%	1000.00%
Derivative Asset (Liability) Net, Measurement Input	0.03	0.04
Fair Value Inputs [Abstract]
Forward power price assets	9	12
Forward gas price assets	0.83	0.78
Renewable factor	91.00%	86.00%
Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Discounted Cash Flow [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	1000.00%	1100.00%
Derivative Asset (Liability) Net, Measurement Input	0.07	0.08
Fair Value Inputs [Abstract]
Forward power price assets	180	174
Forward gas price assets	10.72	12.38
Renewable factor	123.00%	120.00%
Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Option Model Valuation Technique [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.08	0.10
Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Option Model Valuation Technique [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	2.36	2.77
Fair Value, Inputs, Level 3 [Member] \| Proprietary Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ 45,000,000	$ 56,000,000
Fair Value, Inputs, Level 3 [Member] \| Proprietary Trading [Member] \| Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	25	14
Fair Value, Inputs, Level 3 [Member] \| Proprietary Trading [Member] \| Discounted Cash Flow [Member] \| Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	180	174
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ 307,000,000	$ 618,000,000
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted	214,000,000	76,000,000
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Economic Hedges [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value	$ 558,000,000	$ 443,000,000
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	9	12
Forward gas price assets	0.83	0.78
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Discounted Cash Flow [Member] \| Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	180	174
Forward gas price assets	10.72	12.38
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Option Model Valuation Technique [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.08	0.10
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Option Model Valuation Technique [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset (Liability) Net, Measurement Input	2.36	2.77
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Proprietary Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ 45,000,000	$ 56,000,000
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Proprietary Trading [Member] \| Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	25	14
Exelon Generation Co L L C [Member] \| Fair Value, Inputs, Level 3 [Member] \| Proprietary Trading [Member] \| Discounted Cash Flow [Member] \| Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	180	174
Commonwealth Edison Co [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value	$ (301,000,000)	$ (249,000,000)
Commonwealth Edison Co [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	900.00%	1000.00%
Derivative Asset (Liability) Net, Measurement Input	0.03	0.04
Fair Value Inputs [Abstract]
Renewable factor	91.00%	86.00%
Commonwealth Edison Co [Member] \| Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Discounted Cash Flow [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Forward Heat Rate	1000.00%	1100.00%
Derivative Asset (Liability) Net, Measurement Input	0.07	0.08
Fair Value Inputs [Abstract]
Renewable factor	123.00%	120.00%

Cash collateral posted related to credit risk.

No definition available.

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- Definition

This element represents the forward power market price used to calculate the change in fair value of the derivative instrument.

+ References

No definition available.

+ Details

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- Definition

This element represents the factor that is multiplied with the forward price of natural gas to calculate a forward power curve. Natural gas has greater liquidity tenor than power and is commonly used to calculate this curve.

+ References

No definition available.

+ Details

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- Definition

This element represents the forward power market price used to calculate the change in fair value of the derivative instrument.

+ References

No definition available.

+ Details

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- Definition

This element represents a factor to adjust an around the clock forward power price and quantity to be in line with an applicable renewable facility. Solar units generally produce more power in the summer days and wind units generally produce more power in the spring and fall evenings.

+ References

No definition available.

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- Definition

Value of input used to measure net derivative asset (liability).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
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- Definition

Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Section 50
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- Definition

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 815
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Balance Type:	credit
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- 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.

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- References

No definition available.

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