Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	$ 1,365		$ 1,279
Mark-to-market derivative assets (noncurrent assets)	758		773
Mark-to-market derivative liabilities (current liabilities)	(205)		(234)
Mark-to-market derivative liabilities (noncurrent liabilities)	(374)		(403)
Total mark-to-market derivative net assets (liabilities)	5		(3)
Total cash collateral received net of cash collateral posted			1,406
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,365		1,276
Mark-to-market derivative assets (noncurrent assets)	733		771
Mark-to-market derivative liabilities (current liabilities)	(182)		(214)
Mark-to-market derivative liabilities (noncurrent liabilities)	(150)		(105)
Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(23)		(20)
Mark-to-market derivative liabilities (noncurrent liabilities)	(224)		(187)
Proprietary Trading [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	108		456
Mark-to-market derivative assets (noncurrent assets)	22		56
Total mark-to-market derivative assets	130		512
Mark-to-market derivative liabilities (current liabilities)	(94)		(468)
Mark-to-market derivative liabilities (noncurrent liabilities)	(33)		(64)
Total mark-to-market derivative liabilities	(127)		(532)
Total mark-to-market derivative net assets (liabilities)	3		(20)
Collateral And Netting [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(3,994)	[1]	(4,184)	[2]
Mark-to-market derivative assets (noncurrent assets)	(1,163)	[1]	(1,112)	[2]
Total mark-to-market derivative assets	(5,157)	[1]	(5,296)	[2]
Mark-to-market derivative liabilities (current liabilities)	4,827	[1]	5,200	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)	1,564	[1]	1,502	[2]
Total mark-to-market derivative liabilities	6,391	[1]	6,702	[2]
Total mark-to-market derivative net assets (liabilities)	1,234	[1]	1,406	[2]
Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,350		1,264
Mark-to-market derivative assets (noncurrent assets)	719		765
Total mark-to-market derivative assets	2,069		2,029
Mark-to-market derivative liabilities (current liabilities)	(197)		(235)
Mark-to-market derivative liabilities (noncurrent liabilities)	(366)		(289)
Total mark-to-market derivative liabilities	(563)		(524)
Total mark-to-market derivative net assets (liabilities)	1,506		1,505
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	1,350	[3]	1,264	[4]
Mark-to-market derivative assets (noncurrent assets)	719	[3]	765	[4]
Total mark-to-market derivative assets	2,069	[3]	2,029	[4]
Mark-to-market derivative liabilities (current liabilities)	(174)	[3]	(215)	[4]
Mark-to-market derivative liabilities (noncurrent liabilities)	(142)	[3]	(102)	[4]
Total mark-to-market derivative liabilities	(316)	[3]	(317)	[4]
Total mark-to-market derivative net assets (liabilities)	1,753	[3]	1,712	[4]
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	5,236		4,992
Mark-to-market derivative assets (noncurrent assets)	1,860		1,821
Total mark-to-market derivative assets	7,096		6,813
Mark-to-market derivative liabilities (current liabilities)	(4,907)		(4,947)
Mark-to-market derivative liabilities (noncurrent liabilities)	(1,673)		(1,540)
Total mark-to-market derivative liabilities	(6,580)		(6,487)
Total mark-to-market derivative net assets (liabilities)	516		326
Current assets collateral offset	(352)		(416)
Noncurrent assets collateral offset	(180)		(171)
Current liabilities collateral offset	(480)		(599)
Collateral Amount Offset Against Fair Value Of Derivative Current Noncurrent Liability	(222)		(220)
Total cash collateral received net of cash collateral posted	1,234
Designated as Hedging Instrument [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets (noncurrent assets)	0	[5]	0	[6]
Total mark-to-market derivative assets	0	[5]	0
Mark-to-market derivative liabilities (current liabilities)	(23)	[5]	(20)	[6]
Mark-to-market derivative liabilities (noncurrent liabilities)	(224)	[5]	(187)	[6]
Total mark-to-market derivative liabilities	(247)	[5]	(207)	[6]
Total mark-to-market derivative net assets (liabilities)	(247)	[5]	(207)	[6]
Total Cash Flow Hedges [Member]
Derivative [Line Items]
Effective portion of changes in fair value	(12)		(31)
Total Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Effective portion of changes in fair value	$ (8)		$ (15)

[1] Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.

[2] Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.

[3] Current and noncurrent assets are shown net of collateral of $352 million and $180 million, respectively, and current and noncurrent liabilities are shown net of collateral of $480 million and $222 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,234 million at December 31, 2015.

[4] Current and noncurrent assets are shown net of collateral of $416 million and $171 million, respectively, and current and noncurrent liabilities are shown net of collateral of $599 million and $220 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,406 million at December 31, 2014.

[5] Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.

[6] Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.