Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Mark-to-market derivative assets, current	$ 2,169	$ 644
Mark-to-market derivative assets, noncurrent	949	555
Mark-to-market derivative liabilities, current	(999)	(295)
Mark-to-market derivative liabilities, noncurrent	(714)	(473)
Total mark-to-market derivative net assets (liabilities)	(3)	2
Margin Deposit Assets	897	209
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Margin Deposit Assets	897	209
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities, current	(18)	(33)
Mark-to-market derivative liabilities, noncurrent	(201)	(268)
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	2,169	639
Mark-to-market derivative assets, noncurrent	943	554
Total mark-to-market derivative assets	3,112	1,193
Mark-to-market derivative liabilities, current	(995)	(293)
Mark-to-market derivative liabilities, noncurrent	(714)	(472)
Total mark-to-market derivative liabilities	(1,709)	(765)
Total mark-to-market derivative net assets (liabilities)	1,403	428
Commodity Contract [Member] | Collateral [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	152	103
Mark-to-market derivative assets, noncurrent	15	64
Total mark-to-market derivative assets	167	167
Mark-to-market derivative liabilities, current	262	131
Mark-to-market derivative liabilities, noncurrent	83	118
Total mark-to-market derivative liabilities	345	249
Total mark-to-market derivative net assets (liabilities)	512	416
Commodity Contract [Member] | Netting [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	(8,923)	(2,261)
Mark-to-market derivative assets, noncurrent	(2,298)	(1,015)
Total mark-to-market derivative assets	(11,221)	(3,276)
Mark-to-market derivative liabilities, current	8,923	2,261
Mark-to-market derivative liabilities, noncurrent	2,298	1,015
Total mark-to-market derivative liabilities	11,221	3,276
Total mark-to-market derivative net assets (liabilities)	0	0
Commodity Contract [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	10,915	2,757
Mark-to-market derivative assets, noncurrent	3,224	1,501
Total mark-to-market derivative assets	14,139	4,258
Mark-to-market derivative liabilities, current	(10,161)	(2,662)
Mark-to-market derivative liabilities, noncurrent	(3,094)	(1,603)
Total mark-to-market derivative liabilities	(13,255)	(4,265)
Total mark-to-market derivative net assets (liabilities)	884	(7)
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	(18)	(33)
Mark-to-market derivative liabilities, noncurrent	(201)	(268)
Total mark-to-market derivative liabilities	(219)	(301)
Total mark-to-market derivative net assets (liabilities)	(219)	(301)
Commodity Contract [Member] | Not Designated as Hedging Instrument, Trading [Member]
Derivative [Line Items]
Mark-to-market derivative assets, current	25	40
Mark-to-market derivative assets, noncurrent	2	4
Total mark-to-market derivative assets	27	44
Mark-to-market derivative liabilities, current	(19)	(23)
Mark-to-market derivative liabilities, noncurrent	(1)	(2)
Total mark-to-market derivative liabilities	(20)	(25)
Total mark-to-market derivative net assets (liabilities)	$ 7	$ 19