Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Mark-to-market derivative assets, current	$ 644	$ 679
Mark-to-market derivative assets, noncurrent	555	508
Mark-to-market derivative liabilities, current	(295)	(247)
Mark-to-market derivative liabilities, noncurrent	(473)	(393)
Total mark-to-market derivative net assets (liabilities)	2	2
Margin Deposit Assets	209	511
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	644	675
Mark-to-market derivative assets, noncurrent	555	508
Mark-to-market derivative liabilities, current	(262)	(215)
Mark-to-market derivative liabilities, noncurrent	(205)	(123)
Margin Deposit Assets	209	511
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities, current	(33)	(32)
Mark-to-market derivative liabilities, noncurrent	(268)	(269)
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	639	675
Mark-to-market derivative assets, noncurrent	554	508
Total mark-to-market derivative assets	1,193	1,183
Mark-to-market derivative liabilities, current	(293)	(236)
Mark-to-market derivative liabilities, noncurrent	(472)	(380)
Total mark-to-market derivative liabilities	(765)	(616)
Total mark-to-market derivative net assets (liabilities)	428	567
Commodity Contract [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	639	675
Mark-to-market derivative assets, noncurrent	554	508
Total mark-to-market derivative assets	1,193	1,183
Mark-to-market derivative liabilities, current	(260)	(204)
Mark-to-market derivative liabilities, noncurrent	(204)	(111)
Total mark-to-market derivative liabilities	(464)	(315)
Total mark-to-market derivative net assets (liabilities)	729	868
Commodity Contract [Member] \| Collateral [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	103	287
Mark-to-market derivative assets, noncurrent	64	122
Total mark-to-market derivative assets	167	409
Mark-to-market derivative liabilities, current	131	357
Mark-to-market derivative liabilities, noncurrent	118	163
Total mark-to-market derivative liabilities	249	520
Total mark-to-market derivative net assets (liabilities)	416	929
Commodity Contract [Member] \| Netting [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(2,261)	(3,190)
Mark-to-market derivative assets, noncurrent	(1,015)	(877)
Total mark-to-market derivative assets	(3,276)	(4,067)
Mark-to-market derivative liabilities, current	2,261	3,190
Mark-to-market derivative liabilities, noncurrent	1,015	877
Total mark-to-market derivative liabilities	3,276	4,067
Total mark-to-market derivative net assets (liabilities)	0	0
Commodity Contract [Member] \| Not Designated as Hedging Instrument, Economic Hedge [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	2,757	3,506
Mark-to-market derivative assets, noncurrent	1,501	1,238
Total mark-to-market derivative assets	4,258	4,744
Mark-to-market derivative liabilities, current	(2,629)	(3,713)
Mark-to-market derivative liabilities, noncurrent	(1,335)	(1,140)
Total mark-to-market derivative liabilities	(3,964)	(4,853)
Total mark-to-market derivative net assets (liabilities)	294	(109)
Commodity Contract [Member] \| Not Designated as Hedging Instrument, Economic Hedge [Member] \| Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	0	0
Mark-to-market derivative assets, noncurrent	0	0
Total mark-to-market derivative assets	0	0
Mark-to-market derivative liabilities, current	(33)	(32)
Mark-to-market derivative liabilities, noncurrent	(268)	(269)
Total mark-to-market derivative liabilities	(301)	(301)
Total mark-to-market derivative net assets (liabilities)	(301)	(301)
Commodity Contract [Member] \| Not Designated as Hedging Instrument, Trading [Member] \| Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	40	72
Mark-to-market derivative assets, noncurrent	4	25
Total mark-to-market derivative assets	44	97
Mark-to-market derivative liabilities, current	(23)	(38)
Mark-to-market derivative liabilities, noncurrent	(2)	(11)
Total mark-to-market derivative liabilities	(25)	(49)
Total mark-to-market derivative net assets (liabilities)	$ 19	$ 48

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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