Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions	Dec. 31, 2016		Dec. 31, 2015
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	$ 917		$ 1,365
Mark-to-market derivative assets (noncurrent assets)	492		758
Derivative Liability, Current	(282)		(205)
Derivative Liability, Noncurrent	(392)		(374)
Total mark-to-market derivative net assets (liabilities)	1		5
Accumulated other comprehensive loss, net	(2,660)		(2,624)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	917		1,365
Mark-to-market derivative assets (noncurrent assets)	476		733
Derivative Liability, Current	(263)		(182)
Derivative Liability, Noncurrent	(153)		(150)
Accumulated other comprehensive loss, net	(54)		(63)
Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative Liability, Current	(19)		(23)
Derivative Liability, Noncurrent	239		(224)
Pepco Holdings LLC [Member] | Predecessor [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)			18
Mark-to-market derivative assets (noncurrent assets)			0
Total mark-to-market derivative assets			18
Derivative Liability, Current			0
Derivative Liability, Noncurrent			0
Total mark-to-market derivative liabilities			0
Total mark-to-market derivative net assets (liabilities)			18
Accumulated other comprehensive loss, net			(36)
Pepco Holdings LLC [Member] | Successor [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0
Accumulated other comprehensive loss, net	0
Proprietary Trading [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	55		108
Mark-to-market derivative assets (noncurrent assets)	21		22
Total mark-to-market derivative assets	76		130
Derivative Liability, Current	(54)		(94)
Derivative Liability, Noncurrent	(25)		(33)
Total mark-to-market derivative liabilities	(79)		(127)
Total mark-to-market derivative net assets (liabilities)	(3)		3
Collateral and Netting | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(2,769)	[1]	(3,994)
Mark-to-market derivative assets (noncurrent assets)	(1,016)	[1]	(1,163)
Total mark-to-market derivative assets	(3,785)	[1]	(5,157)
Derivative Liability, Current	2,964	[1]	4,827
Derivative Liability, Noncurrent	1,150	[1]	1,564
Total mark-to-market derivative liabilities	4,114	[1]	6,391
Total mark-to-market derivative net assets (liabilities)	329	[1]	1,234
Collateral and Netting | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	(2)	[1]	0
Mark-to-market derivative assets (noncurrent assets)	0	[1]	0
Total mark-to-market derivative assets	(2)	[1]	0
Derivative Liability, Current	0	[1]	2
Derivative Liability, Noncurrent	0	[1]	0
Total mark-to-market derivative liabilities	0	[1]	2
Total mark-to-market derivative net assets (liabilities)	(2)	[1]	2
Derivative [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	909		1,350
Mark-to-market derivative assets (noncurrent assets)	472		719
Total mark-to-market derivative assets	1,381		2,069
Derivative Liability, Current	(274)		(197)
Derivative Liability, Noncurrent	(388)		(366)
Total mark-to-market derivative liabilities	(662)		(563)
Total mark-to-market derivative net assets (liabilities)	719		1,506
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	909	[2]	1,350	[3]
Mark-to-market derivative assets (noncurrent assets)	472	[2]	719	[3]
Total mark-to-market derivative assets	1,381	[2]	2,069	[3]
Derivative Liability, Current	(255)	[2]	(174)	[3]
Derivative Liability, Noncurrent	(149)	[2]	(142)	[3]
Total mark-to-market derivative liabilities	(404)	[2]	(316)	[3]
Total mark-to-market derivative net assets (liabilities)	977	[2]	1,753	[3]
Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0	[3]
Mark-to-market derivative assets (noncurrent assets)	0		0	[3]
Total mark-to-market derivative assets	0		0	[3]
Derivative Liability, Current	0		0	[3]
Derivative Liability, Noncurrent	0		0	[3]
Total mark-to-market derivative liabilities	0		0	[3]
Total mark-to-market derivative net assets (liabilities)	0		0	[3]
Derivative [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0
Mark-to-market derivative assets (noncurrent assets)	0
Total mark-to-market derivative assets	0
Derivative Liability, Current	0
Derivative Liability, Noncurrent	0
Total mark-to-market derivative liabilities	0
Total mark-to-market derivative net assets (liabilities)	0
Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	8		15
Mark-to-market derivative assets (noncurrent assets)	20		39
Total mark-to-market derivative assets	28		54
Derivative Liability, Current	(8)		(8)
Derivative Liability, Noncurrent	(4)		(8)
Total mark-to-market derivative liabilities	(12)		(16)
Total mark-to-market derivative net assets (liabilities)	16		38
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	8		15
Mark-to-market derivative assets (noncurrent assets)	4		14
Total mark-to-market derivative assets	12		29
Derivative Liability, Current	(8)		(8)
Derivative Liability, Noncurrent	(4)		(8)
Total mark-to-market derivative liabilities	(12)		(16)
Total mark-to-market derivative net assets (liabilities)	0		13
Economic Hedges [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	3,623		5,236
Mark-to-market derivative assets (noncurrent assets)	1,467		1,860
Total mark-to-market derivative assets	5,090		7,096
Derivative Liability, Current	(3,165)		(4,907)
Derivative Liability, Noncurrent	(1,274)		(1,673)
Total mark-to-market derivative liabilities	(4,439)		(6,580)
Total mark-to-market derivative net assets (liabilities)	651		516
Economic Hedges [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		0	[4]
Total mark-to-market derivative assets	0		0
Derivative Liability, Current	(19)		(23)	[4]
Derivative Liability, Noncurrent	(239)		(224)	[4]
Total mark-to-market derivative liabilities	(258)		(247)	[4]
Total mark-to-market derivative net assets (liabilities)	(258)		(247)	[4]
Economic Hedges [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	2		0	[4]
Mark-to-market derivative assets (noncurrent assets)	0		0	[4]
Total mark-to-market derivative assets	2		0	[4]
Derivative Liability, Current	0		(2)	[4]
Derivative Liability, Noncurrent	0		0	[4]
Total mark-to-market derivative liabilities	0		(2)	[4]
Total mark-to-market derivative net assets (liabilities)	2		(2)	[4]
Corporate, Non-Segment [Member] | Derivative [Member] | Pepco Holdings LLC [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)			18
Mark-to-market derivative assets (noncurrent assets)			0
Total mark-to-market derivative assets			18
Derivative Liability, Current			0
Derivative Liability, Noncurrent			0
Total mark-to-market derivative liabilities			0
Total mark-to-market derivative net assets (liabilities)			18
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Current assets collateral offset	(100)		352
Noncurrent assets collateral offset	(72)		180
Current liabilities collateral offset	(95)		480
Collateral Amount Offset Against Fair Value Of Derivative Current Noncurrent Liability	62		(222)
Total cash collateral received net of cash collateral posted	329		(1,234)
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0
Mark-to-market derivative assets (noncurrent assets)	16
Total mark-to-market derivative assets	16
Derivative Liability, Current	0
Derivative Liability, Noncurrent	0
Total mark-to-market derivative liabilities	0
Total mark-to-market derivative net assets (liabilities)	16
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	0		0
Mark-to-market derivative assets (noncurrent assets)	0		0
Total mark-to-market derivative assets	0		0
Derivative Liability, Current	(7)		(8)
Derivative Liability, Noncurrent	(3)		(8)
Total mark-to-market derivative liabilities	(10)		(16)
Total mark-to-market derivative net assets (liabilities)	(10)		(16)
Designated as Hedging Instrument [Member] | Currency Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	17		10
Mark-to-market derivative assets (noncurrent assets)	11		10
Total mark-to-market derivative assets	28		20
Derivative Liability, Current	(13)		(2)
Derivative Liability, Noncurrent	(8)		(1)
Total mark-to-market derivative liabilities	(21)		(3)
Total mark-to-market derivative net assets (liabilities)	$ 7		$ 17

[1] Exelon, Generation, PHI and DPL 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] Current and noncurrent assets are shown net of collateral of $100 million and $72 million, respectively, and current and noncurrent liabilities are shown net of collateral of $95 million and $62 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $329 million at December 31, 2016.

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