Stock-Based Compensation Plans - Schedule of Stock-based Compensation Expense (Details) - Share-based Payment Arrangement [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 77	$ 208	$ 191
Share-based Payment Arrangement, Expense, Tax Benefit	(20)	(54)	(74)
Share-based Payment Arrangement, Expense, after Tax	57	154	117
Exelon Generation Co L L C [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	37	77	88
Share-based Payment Arrangement, Expense, Tax Benefit	(10)	(20)	(34)
Share-based Payment Arrangement, Expense, after Tax	$ 27	$ 57	$ 54

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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