Derivative Financial Instruments Derivative Financial Instruments - Summary of Cash Collateral and Letters of Credit (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 787	$ 418
Derivative, Collateral, Right to Reclaim Securities	273	367
Derivative, Collateral, Obligation to Return Cash	96	47
Derivative, Collateral, Obligation to Return Securities	58	44
Incremental Collateral For Loss Of Investment Grade Credit Rating	1,481	2,104
Exelon Generation Co L L C [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Collateral, Right to Reclaim Cash	787	418
Derivative, Collateral, Right to Reclaim Securities	273	367
Derivative, Collateral, Obligation to Return Cash	96	47
Derivative, Collateral, Obligation to Return Securities	58	44
Incremental Collateral For Loss Of Investment Grade Credit Rating	$ 1,481	$ 2,104

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Amount of obligation to return securities collateral under master netting arrangements that have not been offset against derivative assets.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Amount of right to receive securities collateral under master netting arrangements that have not been offset against derivative liabilities.

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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.

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