Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Mark-to-market derivative assets, current	$ 568	$ 644
Derivative Asset, Noncurrent	491	555
Mark-to-market derivative liabilities, current	(422)	(295)
Mark-to-market derivative liabilities, noncurrent	(453)	(473)
Margin Deposit Assets	148	209
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	569	639
Derivative Asset, Noncurrent	488	554
Total mark-to-market derivative assets	1,057	1,193
Mark-to-market derivative liabilities, current	(418)	(293)
Mark-to-market derivative liabilities, noncurrent	(454)	(472)
Total mark-to-market derivative liabilities	(872)	(765)
Total mark-to-market derivative net assets (liabilities)	185	428
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	569	644
Derivative Asset, Noncurrent	491	555
Mark-to-market derivative liabilities, current	(392)	(262)
Mark-to-market derivative liabilities, noncurrent	(190)	(205)
Margin Deposit Assets	148	209
Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	569	639
Derivative Asset, Noncurrent	488	554
Total mark-to-market derivative assets	1,057	1,193
Mark-to-market derivative liabilities, current	(387)	(260)
Mark-to-market derivative liabilities, noncurrent	(190)	(204)
Total mark-to-market derivative liabilities	(577)	(464)
Total mark-to-market derivative net assets (liabilities)	480	729
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities, current	(31)	(33)
Mark-to-market derivative liabilities, noncurrent	(264)	(268)
Collateral [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	24	103
Derivative Asset, Noncurrent	45	64
Total mark-to-market derivative assets	69	167
Mark-to-market derivative liabilities, current	49	131
Mark-to-market derivative liabilities, noncurrent	28	118
Total mark-to-market derivative liabilities	77	249
Total mark-to-market derivative net assets (liabilities)	146	416
Netting [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(2,049)	(2,261)
Derivative Asset, Noncurrent	(962)	(1,015)
Total mark-to-market derivative assets	(3,011)	(3,276)
Mark-to-market derivative liabilities, current	2,049	2,261
Mark-to-market derivative liabilities, noncurrent	962	1,015
Total mark-to-market derivative liabilities	3,011	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	2,566	2,757
Derivative Asset, Noncurrent	1,400	1,501
Total mark-to-market derivative assets	3,966	4,258
Mark-to-market derivative liabilities, current	(2,472)	(2,629)
Mark-to-market derivative liabilities, noncurrent	(1,179)	(1,335)
Total mark-to-market derivative liabilities	(3,651)	(3,964)
Total mark-to-market derivative net assets (liabilities)	315	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	(31)	(33)
Mark-to-market derivative liabilities, noncurrent	(264)	(268)
Total mark-to-market derivative liabilities	(295)	(301)
Total mark-to-market derivative net assets (liabilities)	(295)	(301)
Not Designated as Hedging Instrument [Member] \| Exelon Generation Co L L C [Member] \| Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	28	40
Derivative Asset, Noncurrent	5	4
Total mark-to-market derivative assets	33	44
Mark-to-market derivative liabilities, current	(13)	(23)
Mark-to-market derivative liabilities, noncurrent	(1)	(2)
Total mark-to-market derivative liabilities	(14)	(25)
Total mark-to-market derivative net assets (liabilities)	$ 19	$ 19

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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