Revenue from Contracts with Customers - Change in Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Line Items]
Contract Assets	$ 170	$ 187	$ 283
Contract Liabilities	26	27	35
Consideration (received) due, contract assets	(109)	(146)
Consideration received (due), contract liabilities	65	179
Revenues recognized, contract assets	92	50
Revenues recognized, contract liabilities	(66)	(187)
Exelon Generation Co L L C [Member]
Change in Contract with Customer, Asset and Liability [Line Items]
Contract Assets	170	187	283
Contract Liabilities	48	42	$ 35
Consideration (received) due, contract assets	(109)	(146)
Consideration received (due), contract liabilities	198	465
Revenues recognized, contract assets	92	50
Revenues recognized, contract liabilities	$ (192)	$ (458)

[Line Items] for Change in Contract with Customer, Asset and Liability [Table]

No definition available.

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- Definition

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (b)
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- Definition

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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- Definition

Amount of decrease in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time from transfer to receivable due to right to consideration becoming unconditional.

+ References

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- Definition

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from contract modification which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

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- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

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