Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Mark-to-market derivative assets, current	$ 1,507	$ 644
Derivative Asset, Noncurrent	665	555
Mark-to-market derivative liabilities, current	(1,717)	(295)
Mark-to-market derivative liabilities, noncurrent	(721)	(473)
Margin Deposit Assets	(2,084)	(209)
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	1,505	639
Derivative Asset, Noncurrent	661	554
Total mark-to-market derivative assets	2,166	1,193
Mark-to-market derivative liabilities, current	(1,710)	(293)
Mark-to-market derivative liabilities, noncurrent	(720)	(472)
Total mark-to-market derivative liabilities	(2,430)	(765)
Total mark-to-market derivative net assets (liabilities)	(264)	428
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	1,505	644
Derivative Asset, Noncurrent	664	555
Mark-to-market derivative liabilities, current	(1,709)	(262)
Mark-to-market derivative liabilities, noncurrent	(511)	(205)
Margin Deposit Assets	(2,084)	(209)
Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	1,505	639
Derivative Asset, Noncurrent	661	554
Total mark-to-market derivative assets	2,166	1,193
Mark-to-market derivative liabilities, current	(1,705)	(260)
Mark-to-market derivative liabilities, noncurrent	(511)	(204)
Total mark-to-market derivative liabilities	(2,216)	(464)
Total mark-to-market derivative net assets (liabilities)	(50)	729
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities, current	(5)	(33)
Mark-to-market derivative liabilities, noncurrent	(209)	(268)
Collateral [Member] \| Commodity Contract [Member] \| External Counterparties
Derivative [Line Items]
Cash Collateral Posted	1
Cash Collateral Held		(15)
Collateral [Member] \| Commodity Contract [Member] \| Affiliates
Derivative [Line Items]
Cash Collateral Posted	71
Collateral [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(790)	103
Derivative Asset, Noncurrent	(201)	64
Total mark-to-market derivative assets	(991)	167
Mark-to-market derivative liabilities, current	(559)	131
Mark-to-market derivative liabilities, noncurrent	(95)	118
Total mark-to-market derivative liabilities	(654)	249
Total mark-to-market derivative net assets (liabilities)	(1,645)	416
Collateral [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member] \| External Counterparties
Derivative [Line Items]
Cash Collateral Posted	1
Cash Collateral Held		(15)
Collateral [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member] \| Affiliates
Derivative [Line Items]
Cash Collateral Posted	71
Collateral [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member] \| Commonwealth Edison Co [Member]
Derivative [Line Items]
Cash Collateral Posted	50
Netting [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(17,399)	(2,261)
Derivative Asset, Noncurrent	(2,755)	(1,015)
Total mark-to-market derivative assets	(20,154)	(3,276)
Mark-to-market derivative liabilities, current	17,399	2,261
Mark-to-market derivative liabilities, noncurrent	2,755	1,015
Total mark-to-market derivative liabilities	20,154	3,276
Total mark-to-market derivative net assets (liabilities)	0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	19,631	2,757
Derivative Asset, Noncurrent	3,612	1,501
Total mark-to-market derivative assets	23,243	4,258
Mark-to-market derivative liabilities, current	(18,490)	(2,629)
Mark-to-market derivative liabilities, noncurrent	(3,168)	(1,335)
Total mark-to-market derivative liabilities	(21,658)	(3,964)
Total mark-to-market derivative net assets (liabilities)	1,585	294
Not Designated as Hedging Instrument, Economic Hedge [Member] \| Commonwealth Edison Co [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	0	0
Derivative Asset, Noncurrent	0	0
Total mark-to-market derivative assets	0	0
Mark-to-market derivative liabilities, current	(5)	(33)
Mark-to-market derivative liabilities, noncurrent	(209)	(268)
Total mark-to-market derivative liabilities	(214)	(301)
Total mark-to-market derivative net assets (liabilities)	(214)	(301)
Not Designated as Hedging Instrument, Trading [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	63	40
Derivative Asset, Noncurrent	5	4
Total mark-to-market derivative assets	68	44
Mark-to-market derivative liabilities, current	(55)	(23)
Mark-to-market derivative liabilities, noncurrent	(3)	(2)
Total mark-to-market derivative liabilities	(58)	(25)
Total mark-to-market derivative net assets (liabilities)	$ 10	$ 19

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