Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Mark-to-market derivative assets, current	$ 749	$ 644
Derivative Asset, Noncurrent	443	555
Mark-to-market derivative liabilities, current	(719)	(295)
Mark-to-market derivative liabilities, noncurrent	(554)	(473)
Margin Deposit Assets	(858)	(209)
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	748	639
Derivative Asset, Noncurrent	438	554
Total mark-to-market derivative assets	1,186	1,193
Mark-to-market derivative liabilities, current	(713)	(293)
Mark-to-market derivative liabilities, noncurrent	(553)	(472)
Total mark-to-market derivative liabilities	(1,266)	(765)
Total mark-to-market derivative net assets (liabilities)	(80)	428
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	749	644
Derivative Asset, Noncurrent	441	555
Mark-to-market derivative liabilities, current	(695)	(262)
Mark-to-market derivative liabilities, noncurrent	(311)	(205)
Margin Deposit Assets	(858)	(209)
Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	748	639
Derivative Asset, Noncurrent	438	554
Total mark-to-market derivative assets	1,186	1,193
Mark-to-market derivative liabilities, current	(690)	(260)
Mark-to-market derivative liabilities, noncurrent	(311)	(204)
Total mark-to-market derivative liabilities	(1,001)	(464)
Total mark-to-market derivative net assets (liabilities)	185	729
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities, current		(33)
Mark-to-market derivative liabilities, noncurrent		(268)
Collateral [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(241)	103
Derivative Asset, Noncurrent	(92)	64
Total mark-to-market derivative assets	(333)	167
Mark-to-market derivative liabilities, current	(177)	131
Mark-to-market derivative liabilities, noncurrent	(42)	118
Total mark-to-market derivative liabilities	(219)	249
Total mark-to-market derivative net assets (liabilities)	(552)	416
Netting [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(5,616)	(2,261)
Derivative Asset, Noncurrent	(1,477)	(1,015)
Total mark-to-market derivative assets	(7,093)	(3,276)
Mark-to-market derivative liabilities, current	5,616	2,261
Mark-to-market derivative liabilities, noncurrent	1,477	1,015
Total mark-to-market derivative liabilities	7,093	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	6,541	2,757
Derivative Asset, Noncurrent	1,997	1,501
Total mark-to-market derivative assets	8,538	4,258
Mark-to-market derivative liabilities, current	(6,075)	(2,629)
Mark-to-market derivative liabilities, noncurrent	(1,739)	(1,335)
Total mark-to-market derivative liabilities	(7,814)	(3,964)
Total mark-to-market derivative net assets (liabilities)	724	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	(23)	(33)
Mark-to-market derivative liabilities, noncurrent	(242)	(268)
Total mark-to-market derivative liabilities	(265)	(301)
Total mark-to-market derivative net assets (liabilities)	(265)	(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	64	40
Derivative Asset, Noncurrent	10	4
Total mark-to-market derivative assets	74	44
Mark-to-market derivative liabilities, current	(54)	(23)
Mark-to-market derivative liabilities, noncurrent	(7)	(2)
Total mark-to-market derivative liabilities	(61)	(25)
Total mark-to-market derivative net assets (liabilities)	$ 13	$ 19

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