Revenue from Contracts with Customers - Prior Year Contract Revenues Recognized in Current Year (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Prior Year Revenue Recognized [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 27	$ 18	$ 11
Exelon Generation Co L L C [Member]
Prior Year Revenue Recognized [Line Items]
Contract with Customer, Performance Obligation Satisfied in Previous Period	$ 64	$ 32	$ 11

Amount of revenue recognized from performance obligation satisfied or partially satisfied in previous reporting periods. Includes, but is not limited to, change in transaction price.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12A
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL108322424-203045

Name:	us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration