Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Jun. 30, 2017		Dec. 31, 2016
Derivative [Line Items]
Mark-to-market derivatives assets		$ 833		$ 917
Derivative Asset, Noncurrent		464		492
Derivative Liability, Current		(244)		(282)
Derivative Liability, Noncurrent		(417)		(392)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		833		917
Derivative Asset, Noncurrent		453		476
Derivative Liability, Current		(225)		(263)
Derivative Liability, Noncurrent		(180)		(153)
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		6		8
Derivative Asset, Noncurrent		13		20
Total mark-to-market derivative assets		19		28
Derivative Liability, Current		(10)		(8)
Derivative Liability, Noncurrent		(1)		(4)
Derivative Liability		11		12
Total mark-to-market derivative net assets (liabilities)		8		16
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		6		8
Derivative Asset, Noncurrent		2		4
Total mark-to-market derivative assets		8		12
Derivative Liability, Current		(10)		(8)
Derivative Liability, Noncurrent		(1)		(4)
Derivative Liability		11		12
Total mark-to-market derivative net assets (liabilities)		(3)		0
Collateral And Netting [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[1]	(2,429)	[2]	(2,769)	[3]
Derivative Asset, Noncurrent	[1]	(1,308)	[2]	(1,016)	[3]
Total mark-to-market derivative assets	[1]	(3,737)	[2]	(3,785)	[3]
Derivative Liability, Current	[1]	2,732	[2]	2,964	[3]
Derivative Liability, Noncurrent	[1]	1,490	[2]	1,150	[3]
Derivative Liability	[1]	(4,222)	[2]	(4,114)	[3]
Total mark-to-market derivative net assets (liabilities)	[1]	485	[2]	329	[3]
Collateral And Netting [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		(11)	[4]	(13)
Derivative Asset, Noncurrent		(2)	[4]	(8)
Total mark-to-market derivative assets		(13)	[4]	(21)
Derivative Liability, Current		11		14
Derivative Liability, Noncurrent		2		9
Derivative Liability		(13)		(23)
Total mark-to-market derivative net assets (liabilities)		0		2
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		0		0
Derivative Asset, Noncurrent		0		0
Total mark-to-market derivative assets		0		0
Derivative Liability, Current		0		(7)
Derivative Liability, Noncurrent		0		(3)
Derivative Liability		0		10
Total mark-to-market derivative net assets (liabilities)		0		(10)
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		0		0
Derivative Asset, Noncurrent		11		16
Total mark-to-market derivative assets		11		16
Derivative Liability, Current		0		0
Derivative Liability, Noncurrent		0		0
Derivative Liability		0		0
Total mark-to-market derivative net assets (liabilities)		11		16
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		3,198		3,623
Derivative Asset, Noncurrent		1,736		1,467
Total mark-to-market derivative assets		4,934		5,090
Derivative Liability, Current		(2,895)		(3,165)
Derivative Liability, Noncurrent		(1,644)		(1,274)
Derivative Liability		4,539		4,439
Total mark-to-market derivative net assets (liabilities)		395		651
Not Designated as Hedging Instrument, Economic Hedge [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		14		17
Derivative Asset, Noncurrent		3		11
Total mark-to-market derivative assets		17		28
Derivative Liability, Current		(17)		(13)
Derivative Liability, Noncurrent		(3)		(8)
Derivative Liability		20		21
Total mark-to-market derivative net assets (liabilities)		(3)		7
Not Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		58		55
Derivative Asset, Noncurrent		23		21
Total mark-to-market derivative assets		81		76
Derivative Liability, Current		(52)		(54)
Derivative Liability, Noncurrent		(25)		(25)
Derivative Liability		77		79
Total mark-to-market derivative net assets (liabilities)		4		(3)
Not Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		3	[5]	4
Derivative Asset, Noncurrent		1	[5]	1
Total mark-to-market derivative assets		4	[5]	5
Derivative Liability, Current		(4)	[5]	(2)
Derivative Liability, Noncurrent		0	[5]	(2)
Derivative Liability		4	[5]	4
Total mark-to-market derivative net assets (liabilities)		$ 0	[5]	$ 1

[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] Of the collateral posted/(received), $84 million represents variation margin on the exchanges.

[3] Of the collateral posted/(received), $(158) million represents variation margin on the exchanges.

[4] 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 counterparty exposures subject to a master netting or similar agreement, such as accrued interest, 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.

[5] Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.